I just bought this one:
So far it's okay. The keypad is fairly squashed and is a bit awkward to use because it's laid out in a 'chocolate box style' rather than staggered, but at the same time it's not quite small enough to hold in your hands and reach all of the keys with your hands. The keys feel pretty cheap, but for £20, what do you expect, especially as it has a mouse too : )
However, having said that, now that ICS is here the mouse function works everywhere, not just in certain apps. This gives almost full control of the phone. The only thing missing initially (that I've noticed) was the ability to press 'Menu'. I've solved this by altering the keyboard layout file as per the instrustions here: http://chris.boyle.name/2010/08/android-keymaps
. I chose to re-map the 'Alt Gr' to menu.
By trial and error I'm finding all sorts of Ctrl key combinations to do various things, such as open bookmarks in the web browser (Ctrl B), history (Ctrl H) and so on.
On the plus side it will be small enough to go in a suitcase to take on holiday along with my MHL cable so I can plug it into tvs in the hotel room. Yeah baby!!!