http://forums.omnigroup.com/showthread.php?t=6189 covers a number of your options with OmniFocus 1.0
OmniFocus 1.1 will allow syncing via WebDAV servers (such as MobileMe). A sneaky peek is available, but it has a lot of potential right now for crashing and destroying your data, so I would discourage a new user from signing up unless it's really a last resort. (By the time it's promoted to a regular beta, we'll have most of those hazards removed.)