Depending on your timeline, you might also consider Flash as a cross-platform option. Here's a list of heavy-hitter companies working to make mobile Flash happen in the near future (includes Google, RIM, Nokia, Sony Ericcson, Palm, Motorola, Samsung, etc.):
http://www.openscreenproject.org/partners/current_partners.html
...a video of some of their CEOs...
http://www.openscreenproject.org/about/
...and how to apply for some of the $10MM that Adobe's seeding into the market:
http://www.openscreenproject.org/developers/get_started.html
