Those of who you fear the SVN instructions for getting bundles, run away now.
There are several nifty bundles out there that for one reason or another aren't in the official subversion repository. To update them, you have to remember to do an 'svn update' for each one. Isn't there an easier way? Yes. Yes there is: svn:externals[1]
cd "/Library/Application Support/TextMate" svn propedit svn:externals Bundles
This will popup your chosen editor. Now simply enter the name of the bundles you want updated followed by a space and then the path to their subversion repo. For example, here's my (short) list:
tAylott_subtleGradient.tmbundle http://textmate.svn.subtlegradient.com/Bundles/tAylott_subtleGradient.tmbund... RubyAndRails-Experimental.tmbundle http://www.eyematz.com/svn/public/TextMate/RubyAndRails-Experimental/RubyAnd...
Note that those are only two very long lines. Save your changes and leave your editor.
Now when you do an 'svn update', it'll automatically fetch changes for the other bundles as well.
Caveat emptor for those of you with commit access: make sure you don't accidentally check in the property changes. We mere mortals don't have to worry about this. ;)
[1]: http://svnbook.red-bean.com/en/1.0/ch07s03.html