Another Option
Another option is to uncheck "Automatically synch new apps" in iTunes. This means you can download (via iTunes on your Mac or PC) as many apps as you want, but to get them on your device you need to select each one when your device is plugged in.
To uncheck "Automatically synch new apps" in iTunes: plug in your device. Open iTunes (or it will automatically open). Select your device on the left hand side. Select "apps" from the top list (Summary / Info / Apps /...). At the bottom of the list of apps is "Automatically synch new apps".
This will turn off automatically synch new apps for both iPad and iPhone apps, which may not be what you want.