Competition is a great thing, even if it's a case of the David (Bing) vs Goliath (Google) of search engines. It is a great day for amateur bloggers as Google search now has the option to filter images by usage rights as per Matt Cutts on Twitter. This new filter now easily lets you choose which images you can freely use for either commercial or non-commercial purposes instead of having to spend time digging through the advanced search option. Apparently, Bing has had this feature (I have not used it enough to have noticed that option) for a while.
To access this feature, simply perform a Google image search, then click on "search tools," then "Usage Rights," and finally one of the five options from the drop down menu.
As usual, nothing is perfect, and per the Google help page, there is a disclaimer:
Before reusing content that you've found, you should verify that its license is legitimate and check the exact terms of reuse stated in the license. For example, most licenses require that you give credit to the image creator when reusing an image. Google has no way of knowing whether the license is legitimate, so we aren't making any representation that the content is actually or lawfully licensed.
This means that while they offer you this service to make your life easier, they also have to keep their lawyers happy. A lot of the material that is usable is under the Common Creators license but it would be a Herculean task to police every single image that lands on Google's search results.