Adena Schutzberg at Directions Mag All Points Blog has the news that MapQuest have introduced their own 'StreetView' service. The new service can be viewed on the main http://www.mapquest.com MapQuest website. MapQuest claim:

• 3D Imagery: 360° horizontal and 160° vertical views of any given image within 360 View on MapQuest.com.
• Side-by-side Imagery: The street map is positioned on side of the screen and 360 View on the other; this puts the location in perspective.
• Simple Navigation: Easily move to a new location by moving the green arrow on the street map.

Once it has loaded it is fairly quick but this is probably due to the relatively low resolution of the images. Coverage is currently limited. For example in the Dallas Fort Worth area, only highways and a few major roads are covered. This contrasts with Google Maps which has had coverage of individual local urban streets for a few years now.

I initially had some trouble getting it started so I think the user interface could be a little bit more intuitive. Once you have the StreetView panel up, the green arrow is easily moved - as claimed.