I bought the Yaris as a commuter. My Dodge Hemi Pickup now is my "utility" vehicle for trips and weekends. The Yaris has completely surprised me; not only am I saving $200+ per month on gas, I am really enjoying driving it. I have the bare bones model; power nothing, not even a radio. It is amazingly peppy and handles great. It it totally simple and utilitarian, yet safe and fun. They're hard to find in some areas, so start looking now.
Handling, interior simplicity, visibility. The interior room is incredible for what it looks like from the outside.
Side curtain airbags should be standard (like the Prius).