Image from The Consumerist
No one likes to see ads, and until advertising companies cotton on to the fact that advertising that people enjoy watching works while annoying or sexed-up advertising doesn't, your only real defense is to block them from displaying. There are a couple of different methods for doing this, depending on your browsing habits.
Of course, this site being ad-supported, I may be shooting myself in the foot here, but frankly if my advertisers want your revenue they should be producing better ads. I'll add a Paypal donation button before I publish this, and if you like my advice here you can feel free to drop me a couple of dollars to keep the lights on. Or not, as you will; this isn't my primary business, and I do fairly well on my own.
If you exclusively, or almost exclusively, use one browser, there will be an ad-blocking extension for that browser that should install in seconds and work the vast majority of the time. Each of the major browsers has their own: Internet Explorer, Firefox, Safari and (my personal primary browser) Chrome. They're all dead-simple to install, and each works very well right out of the box. Should you install these, feel free to throw a couple of dollars into the donation box on each site, if available; this is, most likely, their primary business. I can't speak as to how well they do.
If you use multiple browsers, or use an alternative browser that doesn't already block ads, you have a couple of options. The first, and easiest, is to install the plugin for each individual browser. The second, more complicated but more powerful option, is to install Privoxy. Privoxy not only blocks ads, but can also be used to scrub your incoming and outgoing internet connections in a lot of highly configurable ways. Web sites, these days, are less one object and more a collage of pieces from all over the internet. You'll have locally-stored text, images from some other server, embedded video from Youtube, and ads from some remote location (any one of which could contain a thousand other objects, including malicious code). Privoxy works by passing all web traffic through the local application and selectively denying certain requests; for example, if a web site includes blocked ad content, it allows through all of the requests for the page's own elements--text, images, what-have-you--but blocks those calls to external servers that would send you unwanted things. You can use it to turn off almost anything, although if you screw it up you can use it to turn off all web access, too. I highly recommend it to advanced users and those who want to play with having more control, but if you tell me you broke your computer with it I'll charge you to fix it. That's my primary business.