I have had a Garmin Dakota 20 on my Long Haul Trucker for a year now and I love it. However, if I was buying a new GPS today, I would get the Oregon 450 so I could get the larger screen.

For mounting, I just use the Garmin bike mount and it works fine. I didn't have enough spare room on my handlebars, so I mounted the bike mount to the top of my stem with one of the accessory mounts from PurelyCustom.com: http://www.purelycustom.com/c-162-bi...ry-mounts.aspx

Finally, I recommend that you use a backup/safety tether in addition to the mount. One day I was sloppy when putting the battery cover back on the GPS. A mile down the road my GPS went bouncing into the ditch with the battery cover still firmly attached to my bike. Now I always tether it.