Hey, man. Either one of these will take you to a whole other level in conditioning and give you the tools to keep going.

This http://www.webfects.com/hea/routine.htm is a link to free routines by a former Navy Diver and current Navy fitness instructor that only requires your bodyweight. He'll be coming out with video tapes in the next few weeks.

Also check http://mattfurey.com for a site that you can get an excellent book or videos on conditioning with only using your bodyweight. I actually use a hybrid routine of the two.

If you want to add more resistance, then making a sand bag would be an extremely cheap option. ($25)
Check out http://home.rmi.net/~ian21/Sandbagbasics101.html for directions on how to make a reliabel sand bag and exercises you can do with one.