I have a Garmin etrex Vista Cx.

It has:

• Color screen (1-3/8w x 1-3/4h),
• NiMH capable,
• microSD expandable,
• mount bracket screw boss on back (brackets extra),
• waterproof (but doesn't float, that I know of),
• built-in electronic compass and barometric altimeter (either can be turned on/off independently),
  compass works even when stopped (most GPS, you have to be moving to get a direction)
• downloadble US topo and/or marine maps (@ $80-$100 extra each - don't know about global topo),
• will do turn-by-turn street routing (with CityNav, as mentioned by others),
• will upload tracks/waypoints in .loc file format (don't know about .txt) which can be used by EasyGPS/other freeware as well as Garmin MapSource (with or without maps)

The Vista Cx is smaller than the 60/76 mentioned by others and so it only has an internal patch antena. As a result, signal senstivity does suffer ust a little.
But it will definitely fit in a shirt pocket (overall dim 2-1/4w x 4-1/8h x 1-1/4d).

I really like mine. I've tracked international air flights (15hrs) and still had batt to spare. I also use it for geocaching with the kids and driving directions when I travel to unfamiliar cities. I get about 20-25+ hrs on NiMH or Alkaline batteries (2 x AA). (power usage depends on backlight and compass use)

It has a standard USB 2.0 plug on the back and that same cable can be used to power the unit with a 12V cigarette to USB adapter (very cool).
When connected to PC or external power, it does not use batteries, but will switch if power is interrupted (even more cool).

You could probably home-brew a solar-to-USB power adapter easily enough.
The only drawback is that the USB connector on the back of the Vista Cx is under a waterproof cover. The connection itself is not waterproof. The cable sticks straight out.

If you want to, PM me and I'll e-mail some pics.

I bought mine online from here and got a decent deal (and it was a good site for comparisons).

Hope this is helpful.