I also like Shredder on the Iphone- I think the Elo strengths (I have played it up to 2200ish- I dont think I could tell the difference between 2500 and full strength) seem pretty balanced.

Just set up a regular board grab a clock and play it like a regular opponent. I prefer that to waiting around for a g/30 or something on icc. I figure odds are I am playing a computer anyway 🙂