If you've ever been typing away on Gedit and needed to look for some obscure Gtk reference, then this plugin might be for you. It adds an address bar between the toolbar and main Gedit pane, along with buttons for back, forward, new tab, and, of course, go. If you are currently editing a text file and hit the go button, it'll open a new tab with the page in the address bar. The plugin makes it look like it's integrated, so that one tab could be a text document, another a web page, the next a text document, etc.
Current version: 0.1.0.0.1rc2
You can download the plugin here. Unpack it in ~/.gnome2/gedit/plugins (the directory might not exist, so create it if neccessary) or /usr/share/gedit-2/plugins. It will show up in Gedit's list of plugins as "Web Browser."
It's not really integrated, and could conflict with other plugins that do things certain things like adding other widgets to Gedit's main VBox. Also, doing things like saving and printing the "current document" when it is actually a web page will do so to a blank document, because Gedit itself doesn't actually know about the web page.