I think they're great, people seem to love or hate them, they can take a while to get used to, but compared to drawing with a mouse, vast improvement.

I've been using an old A6 Wacom Graphire 2, and haven't had any bother with it. I don't think they make them anymore, though their 'Bamboo' (not made out of bamboo I hasten to add) looks like a perfectly serviceable tablet. If you're not planning on doing any direct tracing (i.e. if you'll be looking at the cursor on the screen rather than at a bit of paper on the tablet) then I don't think there's much point in going over A5, as I think it gets a bit self defeating unless you'e got a large monitor.

A quick look about on the net shows Maplins are doing an alright looking tablet for £30, and ebay has a few Wacom Bamboo tablets for about the same.