This might seem VERY obvious to some but since I didn't find it in the hints archive I thought I'd post it.
I just discovered that you can quickly send attachments just by dropping the file either on Entourage's or Mail.app's icon. You will get a new message window only waiting for the recipient's address, with the file attached. Fast and neat. :-)
[Editor's note: Amazing ... thousands of hours of OS X use, and had I ever tried this? Nope! Cool tip!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021016070333780