Following on from the SFIV and Football Manager deals, Sega have seen fit to slash the Sonic prices and donate the proceeds.
"::FROM NOW THROUGH 3/20, 100% OF SEGA'S PROCEEDS FROM SONIC THE HEDGEHOG iOS TITLES WILL BE DONATED TO THE RED CROSS DISASTER RELIEF EFFORTS IN JAPAN::"
Sonic Spinball £0.59
Sonic The Hedgehog - £1.19
Sonic The Hedgehog 2 - £1.79
Sonic The Hedgehog 4: Episode 1 - £2.39
Spinball in particular works really well and you can play a decent game whilst having that warm feeling of having done something good. :)