I don't really know. The new SLX group from shimano is nice and cheap, the cranks are real light and stronger that XT. Use a 2 ring plus bashguard crankset, SLX front deraileur, X.7 shifters and rear deraileur, if you like SRAM, or go SLX all the way if you prefer Shimano.
Brakes, use Avid Code or Elixir Rs, pretty good and not that expensive. I guess they should be around 130-150 each (depending on rotor size). I have Magura Louise BAT and they work pretty good as well. Shimano XT have received good opinion (I had previous XT model and they were good). Maybe the SLX are almost as good but not as blingy and maybe something less, but I'm betting they're pretty good for a budget.
Forks, probably the Rock Shox Domain is a solid fork, not as nice as the Lyric or Totem, but costs about half of them. 400 bucks and up. I think that the 2009 Marzocchis 55 have worked fine, but actually I haven't heard any bad about them (2008 were not that good quality wise, but 2009 I think they are fine). Fox 36 Van R is also a good option, pretty strong.
Wheelset, well, I guess you could look at around 400 bucks upwards.
You still need a saddle (from 50 to 100), grips (10 to 20 bucks), stem, handlebar, seatpost.
If you're buying new, you could consider Transition prices for forks and component Kit, that could be a good option.