Cydia is full of useful applications and it will be bias to say any single application my favorite application. Though installous is one of the top iphone application which you can download from Cydia.
The work of the installous is to find *.ipa files and all the application of iPhone are in *.ipa format.
How to download and install Installous from Cydia
To download and install Installous, you need to add a source into Cydia. Open Cydia >Manage >Sources >edit >add and enter “Cydia.hackulo.us”.
See the screenshot for better understanding
Once Installous is Installed go to menu and open installous to use it.
Now enjoy the power of Installous and download your fav iphone applications.
Update: Installous is not updated to version 5 and you can read a complete tutorial here: How to download and Install Installous 5
Do let us know if you have more tip to share.