Chrome/Firefox/Opera (in Linux): Websites will often provide the
apt-get command for installing a piece of software on Linux. This Greasemonkey script will turn those commands into clickable links, so you can install those apps with one click of the mouse.It won't turn other Terminal commands into links, so if you need to add a new repository or anything like that, you'll still have to open up the Terminal yourself. However, if you're browsing the web looking for software and you see something you like that's in a repository you have installed, you can just click the apt-get link in your browser to install it right then and there.
Sadly, it seems to be having some trouble on some Lifehacker posts, but elsewhere on the net it works pretty well! Check out VLC's download page if you want to test it out.
Apt-Linker is a free Greasemonkey script, works in Chrome, Firefox with Greasemonkey, and Opera on Linux.