If you don't want to spend a lot of money but still want a very Cintiq-like experience (genuine Wacom digitizer is a MUST!) then look into a Motion Computing LE1600 or LE1700.
I have an LE1600 and use it for freelance art projects all the time- drawing with it is very nice. Of course, yes, it has an actual Wacom digitizer- there is no substitute. No one else does true pressure sensistivity like Wacom, and that's truly the key to the feel and performance that mimics real paper/pen.
The LE1600 is no powerhouse, but it does run Sketchbook Pro, Art Rage, Painter 12 and other apps actually made for drawing perfectly. Photoshop CS5 runs a little laggy, but then I personally don't like using PS to draw with.
You can find the LE1600's dirt cheap on eBay from $100 to $250 or so easily. I wouldn't pay much more than that for one, and make certain it's complete with pen and all needed accessories. If it'd be used outdoors, then definitely find one with the 'Go Anywhere' screen.
The LE1700 is much better, but also pricer. These run Photoshop no problem. A steal is one for around $300 like
this one on ebay. That's a great tablet he's selling, has the Go Anywhere screen, and the dock is a nice extra.
This lady has one of the best videos I've found of an artist demoing the Motion Tablets- she's actually using the lower-end LS800 and still you can see how well it works vs. an iPad. The LE1x00's are even better with a bigger screen.
http://www.youtube.com/watch?v=zrA9UvZtRFA
If you go for a more recent TPC that's $1,000+, I'd look at the Asus EP121. A friend of mine who is a comic book artist has one and loves it. It enables him to not be tethered to his main 21" Wacom setup.
Despite any hype, no other type of tablet actually works well for drawing if it has a touch screen, and not a pen with a real Wacom digitizer.