Thunderbird? Sylpheed-Claws? Uhhhh...not finger-friendly, would really need a UI overhaul for a 3.5" screen. Thunderbird would be pretty resource-intensive anyway.

Modest is working pretty well for me, better than Android email clients ever did. But I am thinking of trying to get Mutt working on my N900. Now THAT would be cool! Lean, mean and fast!