StumbleUpon, the San Francisco startup acquired by eBay (EBAY) in May for $75 million, wants to personalize search – even if you prefer to use sites like Google and Yahoo.

As its name suggests, StumbleUpon helps you “stumble” around the Web and find new content. A downloadable toolbar suggests Web sites and videos and learns your preferences as you give a thumbs up or down to what you see.

On Tuesday the company unveiled SearchReviews, which brings personalized recommendations directly into search results on Google (GOOG), Yahoo (YHOO), MSN, AOL, Ask, Flickr, Wikipedia and YouTube. A registered user simply searches on one of the above sites. If any of the resulting websites have been reviewed by the StumbleUpon community, they will be denoted by a logo, star rating and link to user reviews.

So far StumbleUpon users have reviewed 13 million Web sites. Sixty-five percent of all search queries will include some recommended links and that number should grow as more people use the service.

The stumbling technology could eventually be a welcome innovation for the startup’s parent company. As eBay faces a dropoff in sales growth in its domestic online auction business, SearchReviews could potentially help people window shop on eBay and discover products they wouldn’t have found otherwise.

StumbleUpon CEO Garrett Camp says he can see SearchReviews enabling eBay users to “stumble across the marketplace” to find merchandise or sellers recommended by others. That kind of integration, he says, likely won’t take place for another six months to a year. “We want to let it grow on StumbleUpon first,” says Camp. He notes the the technology will need some tweaking so that it doesn’t, for instance, recommend merchandise in auctions that have expired.

For now the startup is launching SearchReviews without the collaboration of the search giants. Camp says that StumbleUpon can do this because it’s not reordering search results, which would interfere with the search engines’ revenue models.

StumbleUpon currently boasts more than 3.7 million registered “stumblers” that use the company’s website and downloadable toolbar. The company earns advertising revenue by targeting users and sending them directly to sponsored results that have been inserted into the mix of content.

Camp says the new SearchReviews feature was born of the realization that the company can’t compete with the major players like Google and Yahoo. “But StumbleUpon can improve what’s already there,” he says.