Clean lion install - back up apps

[antdawe]

I want to do a clean install of lion on my iMac. How can I back up my apps as I don't have discs/install files for many of them?

I have an external hard drive to put backed up data on.

I don't want to use time machine as my iMac has become severely sluggish and it's an upgrade from snow leopard. I want a clean install but want to keep my apps