Now you can search Yahoo and Google all from one page using Yagoohoogle. It will give you a "split-screen" view of the searches, great for comparing search engines. Now, you might say "I use Dogpile. Doesn't this do the same thing?" No, Dogpile lumps in a bunch of other search engines that don't really give you any thing you need. You end up wasting time looking at stuff you don't need. All you need is Google and Yahoo (in that order) and now with Yagoohoogle you can have them.
UPDATE: Another search engine I really like is SearchThe4. It not only searches Google and Yahoo, but also MSN and AskJeeves. I love the fact that when you scroll one of the "split screen" windows it scrolls the other 4. Its much easier to keep track of where you are on the page.
My only complaints are that when you click a link it opens in the tiny little window, not full screen. As long as you can right click and open in a new tab/window, this may be the search engine for you, especially if you are doing research or need a ton of relevant results fast.
Thanks to Donovan for putting this great link in the comments.
UPDATE UPDATE UPDATE
See this post for new info on this topic.