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.
Meet Your Favorite Search Engine Watch Contributors
Many of SEW's leading expert contributors will be at ClickZ Live, the new online and digital marketing event kicking off in New York (March 31-April 3). Hear from the likes of: Thom Craver, Josh Braaten, Lisa Barone, Simon Heseltine, Josh McCoy, Lisa Raehsler, Greg Jarboe, Dan Cristo, Joseph Kerschbaum, John Gagnon, Eric Enge and more!