This should really be on a meta page called something like ContentFiltering but anyways ...
Here's a very simple hack for getting rid of most ads in your browser using nothing more then a custom CSS file.
For more advanced adblocking capabilities a "filtering proxy" is a high power solution. There are many commercial offerings but good ones are available from the Open Source world such as "The Proxomitron" which works under windows but not linux (unless you use a windows emulator) or "Privoxy" which works under both windows and linux but is harder to personalise.
Most people will want to personalise a filtering proxy so that it doesn't interfere with sites they like and/or use regularly but cuts out the "rubbish" they aren't interested in or dislike. Unfortunately this is different for everyone and it's impossible for the authors of these programs to predict what every individual will want.