I recently bought one, and I chose a Wacom (As it seems universally agreed they are the best) and more specifically the
"Wacom Bamboo Fun Small Graphics Tablet".
The reason was rather simple. It's fairly basic, but has some decent features and a decent level of sensitivity. It is also very well priced considering it's only slightly more expensive than the ones below it, while having a fair few more features. It's also a reasonable size, It says "small", but it seems to be the standard sort of size for tablets that aren't doubled as screens.
As for how well it works? Well I am very much a beginner, so I can't really give a proper review like somebody with experience with multiple tablets can. My only issue is that the pen comes with a button that acts like a right click, and I really wish it didn't, as I keep accidentally pressing it due to how I hold a pen. I'd be much happier without the button and using the mouse when I need it.
You say you want one for casual use and don't want to spend too much. This is a pretty good choice considering it's fairly standard, a reasonable price and is made by what is considered the best company for them.
I also haven't used mine anywhere near as much as I promised myself I would when I bought it... *sighs*