I've been making money for a few years now with Adsense. Ever since I put it on my site it's been making me something. The thing is if you have a website or blog which you have set up and work on anyway, you might as well use something like AdSense. It's really easy to set up and once you do you can pretty much forget about it. It's referred to as "passive income" because once you set it up you don't have to do much at all and you still make money.
I haven't tried AdBrite yet but I just bought and am now reading this book called
AdSense Alternatives which talks about AdBrite and other alternatives - 25 of them in fact. I never knew there were so many.
Of course you can make more if you do tweak and test it, but that doesn't have to be a time consuming thing to do either. There are some really good comments above, so I won't re-iterate on them too much. The key things are to make sure you do your keyword research and get lots of targeted traffic to your site. Provide good content and keep updating your site to keep it fresh in the search engines - although you can get away with doing this less if you have a well-established site with lots of good content.
Have a look at the site in my signature - this is the most valuable membership site I belong to, it solves the problem of traffic to your site and content for your site and the training videos are the best I have seen anywhere. But even if you are not wanting to join it's worth going and having a look at all the free video tutorials and books. This guy really knows his stuff and I have learned more from his videos than from anywhere else. Mind you he has made tons of really good videos - but the information in each is really, really good.