I have to say going Epic with players new to D&D isn't usually a great idea, in my opinion. After all, you can kick all kinds of butt with mid-level (IMX 9-13th level or so) PCs.
That being said, you say epic... but just
how epic are we talking here? Level 21? 27? 40?
Wik's suggestion of Ninja seems the best option, in my opinion. I haven't played a Spellthief yet, but they do look like oodles of fun.
A Diamond Mind/Shadow Hand based Swordsage would be decent at high levels, if you have access tot he
Book of 9 Swords. The Shadow Hand school has a lot of decent shadow-based attacks and tactics and also has a pretty good prestige class associated with it.
There's also the old standby of Rogue/Assassin (if you're evil) or Rogue/Showdancer (if you're not).
Since you're in epic territory, you may also qualify (depending on just how epic your PC is) for a couple of the epic prestige classes (found in the SRD), such as the
Epic Infiltrator or
Perfect Wight.
Still, we need a bit more info. Do you have any ideas about a race you might want to try?