Advanced Find / Replace is a plugin for Gedit (both 2 and 3) for easily search and replace in multiple documents. It currently works with all opened documents and all the files in a directory you select.
When searching in multiple files, the plugin can display a bottom panel (View > Bottom Pane) which displays the row matching your search for each file in the selected directory.
Install Advanced find / replace plugin for Gedit
Installing Advanced Find / Replace is very easy: download the plugin, extract the archive, make "install.sh" executable ("chmod +x install.sh") and then run the install.sh script. Or copy/paste the following commands in a terminal (should work for both Gedit 3 and 2):
cd wget http://advanced-find.googlecode.com/files/advanced_find-3.5.0.tar.gz tar -xvf advanced_find-3.5.0.tar.gz cd src ./install.sh
To install it system-wide instead of just for your user, run the "install_all.sh" script instead (don't run it as root!).
Then you must activate the plugin: go to Edit > Preferences > Plugins and enable "Advanced Find/Replace". Once installed, you'll find it under Search > Advanced Find / Replace.