Have you looked at the mods section linked from the homepage? Decent little feature and lists the majority of good basic mods with user reviews etc.
Power wise, you can go mad. If you think you might soon get used to the 240-250bhp a remap gets you, there are loads of things you can do before the map to gain anything up to about 285bhp and 360lb/ft on the k03 engine (normal GTI). If it's an Edition 30 (k04) the same mods can take you past 350bhp and similar torque. If you want subtle, then a precat delete is useful, along with an uprated panel filter, or for a bit more noise and flow an intake kit (Revo, ITG, Ramair, the list goes on). A bigger downpipe and decat/sport cat will gain more power than a precat. An uprated fuel pump (HPFP) is a great mod on a TFSI (Loba or APR). Then there's bigger intercoolers etc. When you get round to mapping, R-Tech are very good. Fully custom, very smooth, loads of usable torque. Revo are good for tweakable generic maps.
There's loads to list. Have a read of some build threads.
It's worth renewing a few known weak points before upping the power. The diverter valve, pcv and cam follower all wear and can affect reliability and performance. A VW revision G diverter valve is a good option, along with the revision R pcv.
Again, do a search, read up, and you'll get the idea. Good luck!
