http://ex-code.com/gtk2edit/
I have recently reviewed an application you might have heard of called "GTK2
Text Editor" 

despite the authors ill received overly ambitious statements that it could
replace Gedit (and the equally unfair hostile reactions to his attempts to earn
money in return for producing windows binaries) 
GTK 2 Editor is not yet as good as Gedit 
(nowhere near as HIG compliant) 
however it did have one particularly clever thin I liked which was a "Close Tag"
feature, which with a simple keyboard shortcut will automatically create a close
tag for whatever tag you last opened.  

If you had typed <blockquote>you could then with a quick keypress have
</blockquote> added automatically

i think a similar feature could make a good useful plugin for gedit 
(as GTK2 Text Editor is licensed under the GPL it might even be possible to
reuse the code)