I've always wanted someone to create a touch screen device that was the size of a pad of paper. I don't even care how much storage it has, although you can fit more into the form factor then something the size of a phone.
So if it had a touch screen the size of a pad of paper, had an iPhone(ish) interface, had some decent productivity apps, could play music and most importantly surf the web, I'd pay $1,000 to $1,500 for it.
I have a Lenovo X41 tablet that cost me $1000. It's an inch smaller on each side than an 8.5"x11" piece of paper. It has some very decent productivity apps, some of the best, even. It plays music very well and definitely surfs the web. Unfortunately, it runs Windows and GNU's Tomboy doesn't come close to Microsoft's Onenote.
So if it had a touch screen the size of a pad of paper, had an iPhone(ish) interface, had some decent productivity apps, could play music and most importantly surf the web, I'd pay $1,000 to $1,500 for it.