Completely by accident, I've discovered that you can resize drawers (like Mail.app's or Omniweb's) from more locations than just their far edges.
For example: In Mail.app (assuming your drawer is on the right), you can resize the Mailboxes drawer by clicking just to the right of the scrollbar and dragging in either direction.
[robg adds: This seems to work just as well when the drawer is on the left; you just need to click and drag very close to the window edge.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030525115005866