This is some search-plugins i've made.
There are:
google linux
google images
linuxpackages.net
kde-look.org
kde-apps.org
gnome-apps.org
tvtorrents.ws

to use:
put the .src and .png files in ~/.mozilla/firefox/default.vwn/search

at least thats my directory structure in .mozilla

You need to restart firefox to use after putting in the files there...