There's been a spate of "recommend me an ISP threads" lately and at some suggestion I've finally written this. Use this thread to inform yourself before you post such a thread and you'll get considerably more useful answers - I'm inclined to start closing threads where the thread starter clearly hasn't read this (or at least made some effort).
ISPs can basically be grouped into three categories based on the technology they use:
ADSL
There are literally hundreds of ADSL ISPs, and they can be subdivided into two groups - those who use BT Wholesale and those who have their own LLU (Local Loop Unbundling) operation (i.e. have placed their own equipment in the telephone exchange and can have you connected to it). In either case, you're looking at an up to 24Mbps (megabits per second) service.
The first point of call is Samknows. With a phone number and/or postcode, it'll give some idea of what exchange you would be connected to and what LLU services are available. LLU services are typically cheaper, faster and have higher usage allowances than equivalent services via BTw.
Samknows will also give the straight line distance between the postcode you enter and the exchange. There's no real use for the value (dozens of factors can influence what speed you get; the distance is only one and the rest can't easily be estimated before the service is up and running) but it might give an extremely rough guide of what speed you can expect.
Armed with that knowledge, you can then start filtering out ISPs based on features and price.
For starters, unlimited usage is practically non-existent via BT Wholesale because of the costs involved. A few ISPs offer unlimited usage for a lot of money (such as Zen, for £90.75 a month). On the other hand, most LLU providers offer unlimited usage.
Therefore, if your only option is an ISP who use BT Wholesale, you're most likely looking at an ISP who has some kind of usage limit and you need to try to identify your typical usage.
The next part is to think about the features you're looking for. Do you want a contract shorter than 12 months? Free hardware (i.e. wireless modem/router)? More than one public IP address? Free activation (if you don't already have an ADSL service)?
Generally speaking, free activation or hardware you can keep will come with an increased contract term.
Once you've got all that, there are details of ISPs on Thinkbroadband. Beyond that, search this forum and if what you still haven't arrived at an answer, post a thread. You should at least have covered the basic stuff and saved a lot of pointless repetition.
Bear in mind that you need a BT phone line (the voice service does not have to be with BT Retail though) to get ADSL. There's a special case - if you live in Hull, there's a single provider (Karoo/Kingston Communications) and they're your only option.
Cable
There isn't any real choice here: Virgin Media are practically the only cable operator in the UK. There is one other small operator who covers NW England/SW Scotland (Smallworld), but they're forgettable.
You can check whether you can get VM's cable service by sticking your postcode into their web site.
If it says "Because you're in a fibre optic (sic) cable area, you can get all this.", you are in an area covered by Virgin Media's Hybrid Fibre Coax network and can get their cable services which should behave, traffic management aside, as advertised (i.e. the speed you get doesn't have a distance factor as with ADSL).
The one major issue to remember with VM cable is the STM (subscriber traffic management). It's changed a load of times since it was introduced and you can see the latest version of the policy here. In short: download (or upload) more than what VM consider appropriate, and your connection will get slower for a period of time.
If you're not in an area which is covered, Virgin Media will offer you a service over ADSL. Caveat emptor: this service is...not good, certainly not comparable with the cable service.
3G
Pretty much all the networks offer some kind of 3G/mobile broadband service. The one advantage it has over the other two is that you can take the (usually USB) modem or your mobile phone anywhere you like (as long as there's coverage).
The downside is that it's typcally more expensive for regular use (low usage allowances and high overusage charges), slower (potentially significantly so) and coverage (for the fastest speeds) outside cities is patchy at best.
Ofcom has maps showing coverage of the UK by the 3G networks here.
ISPs can basically be grouped into three categories based on the technology they use:
ADSL
There are literally hundreds of ADSL ISPs, and they can be subdivided into two groups - those who use BT Wholesale and those who have their own LLU (Local Loop Unbundling) operation (i.e. have placed their own equipment in the telephone exchange and can have you connected to it). In either case, you're looking at an up to 24Mbps (megabits per second) service.
The first point of call is Samknows. With a phone number and/or postcode, it'll give some idea of what exchange you would be connected to and what LLU services are available. LLU services are typically cheaper, faster and have higher usage allowances than equivalent services via BTw.
Samknows will also give the straight line distance between the postcode you enter and the exchange. There's no real use for the value (dozens of factors can influence what speed you get; the distance is only one and the rest can't easily be estimated before the service is up and running) but it might give an extremely rough guide of what speed you can expect.
Armed with that knowledge, you can then start filtering out ISPs based on features and price.
For starters, unlimited usage is practically non-existent via BT Wholesale because of the costs involved. A few ISPs offer unlimited usage for a lot of money (such as Zen, for £90.75 a month). On the other hand, most LLU providers offer unlimited usage.
Therefore, if your only option is an ISP who use BT Wholesale, you're most likely looking at an ISP who has some kind of usage limit and you need to try to identify your typical usage.
The next part is to think about the features you're looking for. Do you want a contract shorter than 12 months? Free hardware (i.e. wireless modem/router)? More than one public IP address? Free activation (if you don't already have an ADSL service)?
Generally speaking, free activation or hardware you can keep will come with an increased contract term.
Once you've got all that, there are details of ISPs on Thinkbroadband. Beyond that, search this forum and if what you still haven't arrived at an answer, post a thread. You should at least have covered the basic stuff and saved a lot of pointless repetition.
Bear in mind that you need a BT phone line (the voice service does not have to be with BT Retail though) to get ADSL. There's a special case - if you live in Hull, there's a single provider (Karoo/Kingston Communications) and they're your only option.
Cable
There isn't any real choice here: Virgin Media are practically the only cable operator in the UK. There is one other small operator who covers NW England/SW Scotland (Smallworld), but they're forgettable.
You can check whether you can get VM's cable service by sticking your postcode into their web site.
If it says "Because you're in a fibre optic (sic) cable area, you can get all this.", you are in an area covered by Virgin Media's Hybrid Fibre Coax network and can get their cable services which should behave, traffic management aside, as advertised (i.e. the speed you get doesn't have a distance factor as with ADSL).
The one major issue to remember with VM cable is the STM (subscriber traffic management). It's changed a load of times since it was introduced and you can see the latest version of the policy here. In short: download (or upload) more than what VM consider appropriate, and your connection will get slower for a period of time.
If you're not in an area which is covered, Virgin Media will offer you a service over ADSL. Caveat emptor: this service is...not good, certainly not comparable with the cable service.
3G
Pretty much all the networks offer some kind of 3G/mobile broadband service. The one advantage it has over the other two is that you can take the (usually USB) modem or your mobile phone anywhere you like (as long as there's coverage).
The downside is that it's typcally more expensive for regular use (low usage allowances and high overusage charges), slower (potentially significantly so) and coverage (for the fastest speeds) outside cities is patchy at best.
Ofcom has maps showing coverage of the UK by the 3G networks here.