I would eventually like to get a Cintiq but I just got a Samsung Galaxy Note 10.1. It's a little pricey but it's portable and I LOVE it. It comes with a small S Pen and a Photoshop app. The app itself was useless to me as it doesn't support PSDs but after paying $3 for LayerPaint, it's serving me quite well.
You mean an existing one or whatever I can imagine?
From existing ones, a Cintiq.
If I get to be creative... a tablet-PC with a 20" screen with 300ppi display resolution, Cintiq-quality pen input, Core2 i7 -level CPU + appropriate GPU, 64GB DDR3 RAM, full linux support on all hardware. The screen would be OLED, and the device would be light enough to be portable, and would also feature Wifi, USB and Bluetooth for connectivity.
And while we're making wishes, I'd like a million dollars and a birthday cake.
I personally would like an Intuos 5, but they're pretty expensive, even for the small, so that's probably not going to happen any time soon. So I'm probably going to end up with a Bamboo Fun or something similar, but I really don't mind because at this point I just want to get a tablet.
I have an iPad 3 which does almost everything I'd want it to. I'd like to jailbreak it once there's a release for iOS 6.1 since I do feel a tad locked down. The Motorola Xoom that I had before this did every thing I wanted it to do, albeit at a much slower pace, and I was even able to overclock the little bugger after rooting it. Two things I want back most of all though, widgets and console emulators. I need to save the land of Hyrule while laying on my couch.