I would suggest the Asian board game called Go, which you can play online. You can also also play it face to face on the tablet with an opponent using two styli... but be careful not to hover over the board with your styli or the other guy will have trouble making his move. You can get programs that will play against you like SmartGo and Many Faces of Go, but since Go (unlike chess) can't be programed at a high level of play those programs won't offer much of a challenge beyond the beginner level.
Since Go (like chess) won't tax the graphic card or processor it is ideal for play on a tablet, any tablet.
For more information go to www.usgo.org and visit the links in my sig file.