ETasks for iPhone and iPad syncs with MobileMe Beta. Also as MobileMeBeta uses CalDav for events and todo data and because iOS4 allows developers to access this CalDav data, apps can now do over-the-air sync (Wifi and 3G) of todos stored on MobileMe Beta. So far eTasks is the only app that supports this and it works perfectly. The only drawback is that the eTasks interface is kludgy and ugly compared to other todo apps, but the for me the syncing still outweight the ugliness.
What is an utter surprise to me is that eTasks has supported this for several months yet no other app does. Every so often I search the app store for "CalDav", but find no other apps. I'm sure the other major task managers apps that don't use their own desktop app (eg Appigo ToDo and Pocket Informant) must be working on adding these features.
For me the ideal productivity system would be writing my projects in separate notes on the Mac or iPhone and having this sync across Mac and iPhone (which is currently achievable). Then embedding ToDoswithin these project notes (again currently acheivable). However for some bizarre reason Apple considers these embedded ToDoas different from other standalone ToDos, and therefore they won't sync across MobileMe! One major advantage of this system is that project notes are part of your email system and can be archive when they are complete and remain easily accessible not trappedin a proprietary program. The other major advantage of using iCal todos is that it is fast and you can easily drag a todo onto your calendar to plan your week. Weekly planning is so simple using notes > embedded todos > iCal , but Apple just hasn't linked all their software toghether yet!