It isn't cheap compared to standard printers, but the Canon Pixma iP100 has the highest resolution available in the mobile printer market and prints at an impressive speed to boot. If you simply must have a printer with you at all times, the iP100 should be the do-it-all at your side.
The Canon Pixma iP90v is the Vista-enabled version of the older Pixma iP90 and offers nearly the same print speeds and quality. It's a very useful printer if you travel a lot and need to print often, but consider the purchase carefully because it's quite expensive.
With its decent print speeds, serviceable print quality, and great software package, the Canon Pixma iP1800 is a good choice for an inexpensive inkjet printer for home users with basic printing needs.