Rated 5 out of 5 stars

User agent switcher works well and is regularly updated.
A very large of user agents can be imported that goes above and beyond the installed list.Larger List of User Agents for import:
http://forums.chrispederick.com/discussion/7/a-large-regularly-updated-import-list-of-user-agents

or directly at:

http://techpatterns.com/forums/about304.html

Please note 'User Agent Switcher' comes installed with a good list of user agent by default. However, if you want a ton more use the link above.