Part of the allure of handheld computing to both kids and adults are games. There are some great puzzle, logic, and strategy games for both Palm and Windows Mobile. I think the educational value of these types of games are underestimated (take a look at some videos my students did a couple of years back).
While on break, you may be looking for games that are less educational. The best known software company for handheld games is Astraware. Astraware makes addicting games like Bejeweled, Fish Tycoon, Text Twist, and Bookworm, Although you can demo any Astraware game for free, these applications cost between ten and twenty dollars each.
Astraware does off some of their older Palm games for free! Currently there are five free titles offered. Bang! Bang! is a game where you shoot targets to win ammunition and points. Biplane Ace is another shooting game where planes attempt to shoot each other down. Round Up is a strategy/puzzle game where you try to move marbles to their proper places in as few moves as possible. TacTic is similar to Tic Tac Toe. Instead of getting three in a row to win, you are given a larger board and your goal is a get as many points as you can by making the most lines before the board fills up.
The fifth free game may prove to be the most useful in classrooms. T-Blaster is a lot like Giraffe, where you enter Graffiti or type on a keyboard. The objective is to enter the falling text before it hits the ground. This is great for practicing text entry or keyboarding. Like all Astraware games, this one has great graphics.
There is a catch to this free software. You must register the software by supplying Astraware with your handheld's HotSync username. This is easy enough for registering software on one handheld. However, if you plan to use this on a class set of handhelds, be prepared to enter lots of names and registration codes.