www.improveyourchess.com
"The net's first ever chess gym", whatever that means. Ordinarily I'd be skeptical of this site, but I've played Nathan Goldberg a couple of times, he's a reasonable player and a decent bloke; and the GM endorsements are from pretty serious players. Believe it's also the same people who run www.chesspublishing.com, which is a great site - gives some confidence that the money back guarantee will be honoured. Worth checking out. Wish they could have found someone to write better advertising copy.
(I have NO affiliation of any sort with the site - just found it today)