Appulous is a special AppStore for jailbroken iPhones. The problem of the original AppStore is that you can't test the applications. You are mostly dependent on the reviews - if there are some.
Appulous lets you test drive most applications from the AppStore.
To install it, add the following source to Cydia:
http://cydia.hackulo.us . Then install the Installous package
(If you decide to keep an application, buy it from the original AppStore. The developer deserves it.)