World of Solitaire
Everyone and their uncle knows how to play at least one version of solitaire. World of Solitaire includes 22 varieties of the single-player game. That's... that's a lot of solitaire. From the classic Klondike to Scorpion, Pyramid, Yukon and others you probably haven't even heard of, the whole gang is here, complete with instructions on how to play.
Aside from the sheer number of games available, what makes World of Solitaire actually worth playing is the options palette. Don't like the table background? Change it. Don't like the look of the playing cards? Choose a new theme. Want the cards to animate faster, a sharper-looking deck, or the computer to auto-play obvious moves? Go for it. Customize to your heart's content, but don't forget the timer is running and there's a game to be played.
A simple game everyone loves can be ruined with poor design choices, but in the case of World of Solitaire, it can rise to a new level. Forget about that game of solitaire buried on your computer and revisit the classics in style.