One warning though, once you've gone high-end, it's a big stick to swallow to go back down to middle-end or budget...
I went from a HD2600XT 256MB - (overheated and RMAed)
HD2600XT 512MB -
8800GT 512MB -
HD3870 512MB - (Fan bug RMAed)
HD4870 512MB
I don't think I can go back to *middle-tier* anymore... Like a psychological thing right?

I don't even PC game that much at all (Street Fighter IV is so good right now

)
Whereas 5 or 6 years ago any card with 256MB or Radeon would've impressed me and my friends (oh how little we knew).
If I never bought a HD4870, a 1GB HD4850 would've been pretty cool especially at this price. Just be careful peeps, it's a spiral
EDIT: Oh but two of these in crossfire are apparently excellent for performance, so that's something to consider! Especially considering the cost of two HD4870's