Android: Opera 5.1 has left the beta tag behind, and its final release is a considerable Android alternative. Along with the off-phone page caching that makes slower connections bearable, Opera's added semi-solid pinch-to-zoom and kinetic scrolling, plus speed improvements.
As Adam pointed out in his iPhone-based mobile browser speed tests, Opera Mini absolutely flies when it comes to web page loading, though it can be 'rough around the edges. One of the big improvements in Opera 5.1 final is improved image appearance when the page is zoomed out, so that helps with the speed/appearance trade-off, and Opera's also made page navigation a little easier. The pinch-zoom mechanism was a little rough in my early-morning tests, but it's still probably preferable for most users over manual magnifying glass buttons.
Opera 5.1 final is a free download for Android phones, with a QR code offered at the link. Beta users should be able to upgrade from their Market app at the moment.