Opera Mobile 10 includes a handy search bar in the upper-right corner of the browser. By default, there are only two options listed, Google and Wikipedia. The search engine manager gives you the ability to delete, but not add search engines. Considering OM10 is still in beta, it leaves many users thinking that they're stuck with just two choices. In fact, I've seen users question this far too often without any answers in return. It's actually quite easy, in a less clear-cut sort of way, to add more.
To add more search engines to the drop-down menu: first, navigate to the site of the search engine, then locate the search bar on the site, tap & hold on the search field, and you'll be prompted to add it. After it's added, it'll appear in the list.
I've added sites like Bing, Yahoo, eBay, IMDb, YouTube, and more. This eliminates the need to load these pages before searching for keywords, essentially cutting out the middle ground. Tapping and holding on a search field to access this feature can be easily missed, even for those who use Opera Mobile 10 on a daily basis.