One toolbar that's not included in Chris's Firefox overview is one released a few minutes ago.
Clusty's Toolbar for Firefox offers up what you've come to expect from search toolbars along with a context-sensitive searching option called "Clusty Clips." This feature allows the searcher to access definitions and encyclopedia entries (via Wikipedia) and run searches without having to click off of a web page.
Finally, Michael Abramowitz from Yahoo, offers up a Firefox/Yahoo extension on the Yahoo Search Blog.
The Original Search Marketing Event is Back!
SES Denver (Oct 16) offers an intense day of learning all the critical aspects of search engine optimization (SEO) and paid search advertising (PPC). The mission of SES remains the same as it did from the start - to help you master being found on search engines. Early Bird rates extended through Sept 19. Register today!