FireFox
Great web browser with tabbed browsing and built in pop-up blocker

Mozilla
For web browsing, email, HTML editing, IRC chat, and more * Built with your privacy and security in mind * Stop pop-ups and junk mail * Open multiple web pages in the same window with tabbed browsing

Opera
Pop-up blocker * Tabbed browsing * Integrated Google search * Opera Mail with SPAM killer * RSS reader * IRC-compatible chat

Safari
Experience the web, Apple style, with Safari

SeaMonkey
The SeaMonkey project is a community effort to deliver production-quality releases of code derived from the application formerly known as "Mozilla Application Suite". Whereas the main focus of the Mozilla Foundation is on Mozilla Firefox and Mozilla Thunderbird, our group of dedicated volunteers works to ensure that you can have "everything but the kitchen sink" — and have it stable enough for corporate use

Google Toolbar
If you use Internet Explorer you need the Google Toolbar.

Yahoo Toolbar
This Internet Explorer toolbar has both a pop-up blocker and spyware/adware blocker built in.

MSN Toolbar
Tabbed Browsing for Internet Explorer, Form Fill, Pop-up Blocker