MapJack.com is a street-level image viewer mashed-up with Google Maps. The image quality is much better than Google's Streetview, but the 3D feel is not quite as immersive. Personally, I'll trade better image quality for 3D immersiveness. Try "driving" down the famous Lombard Street in San Francisco using MapJack — this is the crookedest street in the US. Currently MapJack only offers views in the heart of San Francisco.
Earthmine also plans to offer high-resolution images at a street-view, but their focus seems to be more on selling this data to companies, governments, etc. They may put a web front-end on the data, but that does not seem to be their focus.
Google Map's "Street View" seems to have unleashed a flood of similar offerings. To be fair, I'm sure that they've all been under development for a while, it's just that the buzz around Google Street View has made them more visible.