Newtonica is perfect.
Trism or Cookie Bonus Solitaire.
Trism uses the accelerometer, which adds a great touch to a Bejeweled-type game.
Cookie Bonus Solitaire is just a straightforward Klondike solitaire, but it has good features and it does what it's supposed to.
I have several games (bought and free) and those are the two I play most often.
Aurora Feint is pretty good too, but it's a memory hog, and not quite as engaging, IMO.