I haven’t had much chance to look for fun flash games for the PlayBook, but I came across a gem on MiniClip.com that works great on the PlayBook browser. I haven’t been able to figure out other games that require a keyboard for movement (although I’ve heard some online games actually makes use of the PlayBook’s accelerometer), but this one is only controlled by left clicking the mouse so it works nicely with the PlayBook’s touchscreen. The only glitch I found is that you are unable to confirm where you place towers, so be careful where you tap.
There are a bunch of unlockable features and cool powerups. Try Canyon Defense on your PlayBook or computer. Let us know if you’ve found any other cool games online that work well with the PlayBook!