I tried Solavant almost immediately after it was first announed -- I'd been looking for a non-cartoony, decent looking and decent playing solitaire game.
At the time, I was less than impressed -- after my first game, I ran into a crash. Mailed the developer, let him know what happened, told him I'd try again in a few months.
Well, I came back, and I'm glad I did. This is easily the best solitaire collection I've found for the Mac; the rules are well presented, the layout is nice, the depth of games is staggering, and the lack of "cheats" is refreshing. I can't recommend this highly enough -- the developer has regularly updated the program. and is very fast with responses to suggestions.