Skyfire
Been using it for a cuople of weeks now - it was cool seeing stuff render and have animations on my TyTN2 - you can even use BBC iPlayer on it and watch the TV through a WiFi connection. It means that I can access websites that previously sent IE mobile utterly crazy. However - it does munch the GPRS data if you're using a mobile session and not WiFi. I don't think its going to replace IE on the phone, but I'll use it for non mobile browser optimised sites - facebook will still be through IE. Although Opera looks good with Facebook mobile....