So far I've only done it on the computer, and that was to go to the App Store, and go to "Login W/ Your Account"
Log in, and you should see your purchases and in bold underline "Download"
With the App Store App
Just go to MyApps, login in, and theirs "Download"
Most purchases from the CB Store are done through Mobihand. Go to their site, login with your e-mail address and password and then go to your apps. You can have them text you the link to redownload the application.