View Single Post 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.)