Here is a common conversation I have when helping people with their computers:
Me: "Wow, you have a lot of toolbars installed. Do you like having those?"
Me: "Do you know where they came from?"
Me: "Do you want me to remove those?"
Them: "Yes, please!"
If you can relate, roll up your sleeves and lets do some spring cleaning!
Step 1: Clean up your browsers
This article shows quite nicely how to remove toolbars from the most prominent browsers. (As of today, these methods worked--keep in mind browsers get updates and instructions might change in the future.)
Step 2: Don't install more toolbars
Where do these toolbars come from? Chances are at some point you installed a program with a toolbar included. Toolbars aren't always malicious--companies like you to see their name plastered where ever possible. For example, notice that when Yahoo!Messenger is installed, the Yahoo! Toolbar will also be installed:
It's all good if you want to have the toolbars installed. Just be aware of the choices that show up during installation and read through the installation process. Cancel and do some research if wording sounds at all fishy.
Step 3: Become more knowledgeable/Dig deeper
Unfortunately, it is possible that just removing the toolbars isn't enough. Some toolbars have bad intentions and can slow down the entire system. I found that Enigma Software Group has an extensive list and explanations of malicious toolbars.
Here is an article that delves deeper into what's behind malicious toolbars, symptoms you may experience, and preventative actions you can take: Sneak Attack--Those Annoying Toolbars You Never Wanted.