For high portability, I already have an N900.

I would like something with a bigger screen and higher pixel count, because that would be much better for reading ebooks and more than casual browsing.

Something with a 6 or 7 inch screen, with a 640x1024 resolution, good for reading, small enough to carry it almost everywhere. It would be perfect if it were of the Pixel Qi variety, to reduce eye strain and save battery power.

I would sacrifice the camera, if needed, but I would like a magnetometer in addition to the accelerometer in the n900, for maps augmented reality applications.

Other than that... It should have good built quality, usb ports and sd/microsd slots for memory expansion.

And it should be cheap.

Build that, and I will buy it.