Arenas? I'm sorry, but getting snubbed for the all-star game doesn't make you underrated. Mike Redd, too.
I like the Gerald Wallace choice, and Brevin Knight, too. Eric Snow was a favorite underrated choice of mine for a long time, but his career's winding down quite a bit. Personally, I love point guards with high A/TO ratios. That, IMHO, is easily the most important stat for a point guard.
My choice right now, though? David West. Averaging almost 17 points and 8 boards a game. And unless you're a New Orleans/OKC fan, I'll bet money you didn't know that. I didn't; I had to look it up.