I haven't used it as a remote whiteboard yet, but I've got a Wacom "Intuos Pen". It's about $80 and it has served as a scrap-piece-of-paper replacement over and over. For sketching out architecture diagrams, web page "mock ups", etc, I have completely fallen in love with it.
Before I got the tablet I mentioned in the sibling comment, I used a stylus with an iPad for a while. It was pretty decent, but whatever software I was using had pretty mediocre palm detection (it'd freak out a bit if I rested my hand on the screen while drawing). I'd also definitely recommend getting a more expensive stylus... the cheap ones I tried generally didn't work well at all.
