i can understand your worry about this, so i've listed all the parts where there is really no reason not to get them from my spec:
(long post warning)
i5 2500k
the two best processors on the market today are the i5 2500k and the i7 2600k. they are totally identical, except the 2600k has hyperthreading. i wont go into the details, but hyperthreading will not help with gaming so it is not orth spending the extra £75 on a feature that you wont use. however it will help with video encoding, large photoshop files, CAD/CAM work, etc.
comparison of the two here:
http://www.anandtech.com/bench/Product/288?vs=287
Silverstone Raven RV02
this case is one of, if not the best for air cooling on the market because of its rotated motherboard. it has fantastic airflow, and has a side window to see all the loveliness inside. the cable tidy features are great, and theres no shortage of hard drive space.
ultimatly, there are lots of very good cases around though, so the most important thing is to choose one you really like the look of, as there isnt a major difference between the top cases.
Corsair XMS3 8GB
4GB is generally considered just fine for gaming, but there are a few games creeping out that will benefit from more. with it only being £62 theres really no reason why not.
this ram was chosen because 1600Mhz is pretty much the sweet spot between speed and value for money. it also has short heatspreaders which mean it will fit under all CPU coolers on the market, unlike RAM with tall heatspreaders like the corsair vengance, and even the Gskill Ripjaw, both of which wont fit under the silver arrow. if the kingston 1600Mhz RAM was cheaper than the corsair i would have chosen that instead
Thermalright silver arrow
the thermalright silver arrow and the Noctua NH-D14 perform remarkably similarly, and are considered to be the best coolers on the market short of getting a custom water cooling system. they beat the more expensive all in one water coolers as well by a reasonable margin. its difficult to find differences between the silver arrow and the D14, but the silver arrow seems to sneak ahead by a whisker. however, with the silver arrow being almost £20 cheaper than the noctua its a no brainer
Mechanical hard drive
generally the recommendation here is to get the cheapest one from a reputable brand, while avoiding a couple of the stray 'slow known brand' hard drives like the F1 series samsung spinpoint. the connection type does not matter as long as it is some form of SATA connection as mechanical hard drives are simply not fast enough to benefit from the faster connection.
Blu Ray drive
i dont know much about these, but getting the retail version is very much recommended because i remember seeing several threads saying what the OEM drives couldnt do but the retail ones could. ask in the optical section if you want
DVD drive
there is very little difference between DVD drives. generally the recommendation is the cheapest DVD +- RW SATA. the OcUK value one is generally avoided in the same way that stuff like tescos own brand beans would be avoided if its the same price as heinz.
i went for the LiteOn simply because there were three different drives that were £16.99, and this one was faster than the other two (24x rather than 22x). the difference wouldnt have been that noticable but the improvement was free so there was no reason not to
as for the rest of the stuff in my build, there are plenty of arguments for and against getting them, but hopefully this will help you with a good chunk of the build
