I assume you mean online MMORPGs like WoW. I don’t do that.
Offline single-player games I’ve enjoyed over the years include the Might&Magic series, the first two Gothics (didn’t manage to play the 3rd one yet) and Neverwinter Nights. Oblivion is surely amazing (as all the previous Elder Scrolls games), though I haven’t managed to play any of those either due to time limitations. And if you’re into retro-gaming, try and find a bugless version of Daggerfall (needs DOS, graphics are quite good though). I also enjoyed all the Quest for Glory games, though these are not pure RPGs in the traditional sense.
The only online RPG I’ve played was Lineage, but I was on a buggy server, so I didn’t enjoy it much. Might be better nowadays.
For browser-based online games, try Dragoncourt (1 or 2) at www.ffiends.com – highly addictive despite the rudimentary graphics. And it’s free (but you cannot go beyond a certain level unless you register).