I recently bought the HTC Hero.
So far so good - impressive array of apps now and I haven't had to pay a penny for any of them. Would have liked to have a flash on the camera, but it's not that much of a worry. (Might feel differently about that once the clocks go back later this month) It has a pretty good video camera too. Has a built in PDF reader, plays adobe flash and can read (but not edit) MSOffice docs. (word, excel, powerpoint)
Fully integrating with Facebook has actually meant I know what my nieces & nephews are up to these days! (And other family abroad etc) I haven't ever used twitter or flickr, but the phone can link to those too.
It seems to me to be the phone equivalent of having a PC with Linux on it as it seems to be very 'tweakable' if you're willing to dive in and have a go.
So far, so pleased.