This hint combines two-rarely used features -- Microsoft Excel's Web Page Preview and Safari's Mail Contents of this Page -- in a useful manner.
Open a spreadsheet in Excel, and choose File: Web Page Preview. Then in Safari, select File: Mail Contents of This Page (or just press Command-I). Surprisingly, the columns format nicely and the HTML code that it sends out will view properly in everything from web-based email clients to Entourage and Outlook. In many cases, this method of sending a spreadsheet may be preferred to sending an attachments.
[robg adds: Both Word and PowerPoint also have the Web Page Preview feature, so you could also send those files in this manner. It might not make much sense for Word, but could be useful for sending out the occasional PowerPoint slide.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2006083009170781