Security

Windows comes on thousands of computers every year. It includes Microsoft's web browser, Internet Explorer. Many people use it because, hey, it's there, and maybe they just don't know of anything else. To the point: thousands of Windows users = thousands of Internet Explorer users = a great target for baddies. Plus Microsoft doesn't seem to be as gung-ho issuing security updates for it as other browser makers are for their browsers.

Standards Compliance

Even if you don't understand all the code that makes web pages go, your browser does. Imagine if your car was the only one in the world that needed banana juice-gasoline mix to make the engine work right. Same idea here; if your browser doesn't comply well with open web standards (such as manged by the W3 Consortium), it's a pain to design for separately. Internet Explorer is notorious for this; it costs web designers plenty of time and grief.

Extendibility and Customization

Internet Explorer is actually making some progress here, but other browsers have it pinned to the ground by comparison. Especially Firefox and other Mozilla based browsers. Imagine an internet task you wish to integrate into your browser; it's likely enough somebody has already made a Firefox add-on for it. This is one of the great powers of alternative browsers - they can be molded to fit the way you use the internet.

And so for those very reasons, I present to you the following alternatives:

Google Chrome

The interface is minimal and clean but has a twist to it; when the window is maximized, the tabs are at the very top. This can make for easy and fast clicking. When it's not maxamized, a little space is inserted between the top of the window and the tabs. Also features: web search from the address bar, one click bookmarking, a hideable bookmarks bar, and thumbnails of recent sites as well as recent bookmarks in new tabs. The engine and interface overall pretty snappy. Add-ons exist but require using the beta version. Themes are supported and there are quite a few to choose from.
-download Google Chrome- Windows (Mac/Linux in development)

Mozilla Firefox

If you've heard of one alternative browser, it's probably Firefox. It wasn't the first, but it was the first in recent times to gain much traction (over 20% market share in May 2009). It has an excellent rendering engine, and many, many add-ons available. They cover a wide varity of tasks: social networking, interface tweaks, userscripting, ad blocking, etcetera. There are also a ton of themes for Firefox, so you can shake things up if you want. It's open source and is available to the major platforms and has also been ported to other, less known operating systems. It is known to eat up a lot of RAM (so can other browsers, but Firefox often gets accused of it), but version 3 did improve this somewhat.
-download Mozilla Firefox- Linux/Mac/Windows/Others

Opera

Opera is a pretty solid browser. The rendering engine is good and performance in other areas the browser is also good. One pretty cool feature is a speed dial panel when you open a new tab; you can bookmark whatever you want on the speed dial and you'll have a thumbnail button for it. The browser itself is a swiss army knife of sorts; mail, IRC, and notes are built in, as well as an adblocker of sorts. Widgets are the easy way of adding on functionality; they actually run in seperate windows from the browser, however, so don't expect integration as tight as Firefox or Chrome. Userscripting is also buried in the options. Themes are supported and there are plenty to go around.
-download Opera- Linux/Mac/Windows/Some mobile platforms

Safari

Safari is based on the same rendering engine as Chrome, WebKit, which gives it some sweet speed. The interface is simple but thorough. It's from Apple; what else can I say?
-download Safari- Mac/Windows

If you're using Internet Explorer, but still not persuaded, please at least make sure you're up to date...

The truth is, too many web users out there are using one particular, outdated browser: Internet Explorer 6. If you use it, I beg you, for your sake and ours, update to IE 8 (or at least 7). You'll need to have at least Windows XP. This will make your browsing experience safer, faster, and generally better (as much as IE can make it). It will also help out web developers, a lot.

So, how can you tell what version of IE you have? Head over to here in IE. Or, open the Help menu (you may have to press the Alt key once to make the menus visible) and click About Internet Explorer.

If this sort of stuff interests you, see also Bring Down IE6.

And if you still want to stick with IE, you can beef it up...

You can actually use a different shell with the same Internet Explorer engine underneath. This is good because these shells have some nice features (meaning stuff IE doesn't have by itself). If you're interested, take a look at IE7Pro and Avant to start with.

By the way, all this stuff is free. Enjoy.