I like the Garmin 52LM. I paid $65 for it from RadioShack. It's not waterproof, so I have it in a sandwich bag - I can still operate it with gloves on and the sandwich bag cover. It turns on when I turn the bike on, and, I have it configured to go right in to map mode when it starts up. When exploring, it's nice to have a map of my surroundings.
I would recommend using a RAM mount, and a Garmin model-specific cradle to mount on the handlebars.
You would need 4 parts to mount it on the handlebar:
- A ram mount with a 1" u-bolt clamp.
- A short universal joint arm.
- A Garmin model specific cradle.
- A ball attachment for the cradle.
Here's a photo of the handlebar mount not including the cradle:
http://www.rammount.com/images/gallery/RAM-B-149ZU/high/RAM-B-149Z.jpgAnd here's what the model specific cradle looks like for my 52LM:
http://www.rammount.com/part/RAM-HOL-GA55UBefore buying one, check to see if RAM has a specific cradle for it - they cover most Garmin models.
Also, if you should buy a used one, try to get a model ending with 'LM' or 'LMT' - those models have free "lifetime" updates for maps (LM) and traffic reports (LMT)