Firefox version 2 was recently released. I haven't had a chance to install it yet, but it is worth checking out.
Firefox is more secure than Internet Explorer, and has more features. Internet Explorer 7 has also been released, but based on the very bad security record of IE, it is not recommended.
Internet Explorer is not very secure and if you use it you may end up with a lot of unwanted spyware. Firefox is a free alternative browser that prevents a lot of problems caused by Internet Explorer.
Why Internet Explorer is Unsafe
Internet Explorer is unsafe partly becuase it uses a feature called ActiveX that can allow software to install on your computer without your permission. A current list of Internet Explorer security flaws can be found on Secunia's Vunerability Report. More information about why Internet Explorer is unsafe can be found on BrowseHappy.com.