Lightweight "Travel" GPS in Direct Sunlight

I'm looking for a GPS that I can put on the handlebar of a moto (small motorcycle) or bicycle when traveling instead of having my Garmin Vista HCx in the carabiner stretch holster (Garmin part 010-10480-00) I've currently been using.  The idea is to be able to view while riding, instead of having to stop/slow down to look at the screen.

Requirements:
--readable in direct sunlight
--waterproof
--relatively lightweight (especially for the bicycle scenarior)
--readable screen
--addon maps.

Other considerations:
--batteries (removable chargable; AA; non-removable)
--screen size
--controls (touch, button, manipulate relatively safely while moving)

Evaluation so far:
--the nuvi 270 isn't readable in direct sunlight as the HCx and 76CSx are, regardless of what I see in online reviews.