If you are a techie, the best freelance/temp work will come from your persistently networking with people and companies that match your interest and expertise. Those may also lead to partnerships or investments or just plain old good advice for your startup.

Of course there can be a lot of difficult balancing required between freelancing and starting up, but many people make it work. The salesmanship, discipline, and customer relations skills you learn freelancing can certainly come in handy in a startup.