Where is the best place for the mods?
I've already got half way through the game and just recently realised that there were loads of mods for it

Where is the best place to grab them? May as well add them
I always got most of mine from the bethesda forums. All the mod devs post there and there are usually lists of must have extra and you can read up about all of them.
Sadly the forums aren't what they used to be now. They used to just be packed full mods and now seem to have more posts about people asking about them instead. I guess most of the devs have moved to skyrim now but I heard all the devs of the overhauls have stopped now because they have been doing them since morrowind:
http://forums.bethsoft.com/forum/45-fallout-3-mods/
What is this FCOM mod and where can I find it? I had a quick look on nexusmods but couldn't see it.
FCOM is a mix of 4 overhaul mods to bring you the best of all of them and within these 4 mods is many other mods as well. It's all customizerble and lets you select options like changing spawn rates etc. For example, M stands for marty's monster mutagen mod and that overhauls the creatures, changing their spawn rates, sizes, stats etc. It brings the world alive by populating it with many more creatures and not ones that look identical.
However, from the looks of it I may have used FWE instead with MMMM. It's not quite the same but I think FCOM went under early on due to the devs wanting a break and I forgot. I certainly remember the name FWE.
If you scroll down the page you will find recommended mods to go with FWE and I highly recommend it. It will changes the game a lot though, the game will be a lot harder. I remember walking into the washington district and there being about 100 mega mutants and having to run away and come back with a minigun

. These mods challenge the player and make you NEED better weapons. A bit like oblivion was a very easy game until these overhaul mods came out:
http://forums.bethsoft.com/topic/10...644991__hl__fcom__fromsearch__1#entry14644991
It also increases damage that both you and your enemies take and the accuracy of guns. You can iron sight people once you get good enough. It really does improve the game 10 fold. I likely used all the recommended mods too, I can't remember now sadly.
It is a modular mod, which is to say you can pick what you do and don't want. It will give you a choice like x2/4/6/8/12/24 for monster respawns, things like that. I highly recommend upping them. The monsters in the wild should fight each other also.