Taking the concept of the Tablet PC to the budget end of the market is the AceCAD DigiMemo A501. It uses an electronic pen with an ordinary nib and a magnetic backing plate to replicate notes you write on ordinary paper.
It will take an A5 pad which slots inside and can be up to 120 sheets thick. After each page is finished you press the down arrows to tell the unit you've started a new one, which stops the digital page getting written over when you start a fresh sheet of paper. It has 8MB of onboard memory and will also accept a CompactFlash card.

The software included is fairly rudimentary, and not very intuitive. It involves a little jiggery-pokery to download the files via USB from the DigiMemo as the Digimemo Manager software doesn't automatically synchronise with the device, instead it relies on Windows to recognise it as a removable drive. Then using the Digital Page option on the dropdown menu you can navigate to the drive letter and select the files -- the obvious Open command won't work.
The device generates its own proprietary file format which can only be read by the driver's software. This isn't a problem unless you want to use the files it generates elsewhere. The Save As option won't work either -- you need to go to the Page dropdown menu and select Save As An Image.

The capture device works most times, and sometimes not. Lighter strokes aren't always captured so you have to press relatively hard to get everything down. This can mean some pen strokes and even whole letters could be lost -- not the best gadget to use to jot down mission critical notes.

This isn't a business tool. It has some usability issues and its plastic construction means it wouldn't handle extended use on the road. It's more of a fun note taker than a Tablet PC replacement.