If I can just mention Bright 0.2b now has over 300 games at 40/40 and appears on the best versions list around 15th place. OK it is a private engine but I was personally interested in testing it (I have run a lot of games for it, and still have a few more coming, and of course there is Graham's gauntlet too)
Zappa Mexico x64 on 1 CPU is almost certainly the number 2 engine on a single CPU, behind Rybka. This could be short lived however - Hiarcs 12 may threaten when it is released by the end of the year (or thereabouts). Maybe Shredder 11 can give it a fright as well, although that will be a bigger leap