I got my iPod touch today and have been trying to find an immediate solution without resorting to buying OmniFocus. I've been using the free version of OmniOutliner a bit and must say I HATE the convoluted formatting functions, powerful as they may be. Maybe I'll get used to it.
CarbonFin Outliner, for iPhone/iPod touch, allows you to sync OmniOutliner files with their Outliner online. It seems pretty kludgy to me, but it might be worth a look.
http://carbonfin.com/
http://outliner.carbonfin.com/