If you have no money, you can also talk to some people and find plenty of stuff to sell. There is a lot of "garbage" (or so most people think it is) that will sell online.
Orginal iPhone 8GB box only and documentations - eBay (item 140326666736 end time Jun-18-09 11:32:12 PDT)

apple iphone 3g 16gb white box - BOX ONLY - - eBay (item 260429421688 end time Jun-22-09 10:33:16 PDT)

Many more boxes than just an iphone box will sell too. Another good thing is broken electronics or incomplete items(items with lost pieces etc). My buddy just ran across a broken ps3 and xbox360 last week. Both were going to be thrown away, when they can be sold on ebay for $100+ parted out. People will pay good money for the parts. Magazines are another freebie that can sell fairly well, usually only worth your time if you sell them in larger lots though.

As for MJs idea, if you are in a place with a decent size college....you should be able to flip furniture extremely quick when everyone comes back for school. I'd go for garage sales though.