The blog Apple Matters has a pretty comprehensive list of tips and tricks for Mac OS X users, from using the Tab key to cycle through open applications in Expose to the hidden power of the option key. A ton of simple keyboard shortcuts and tips are in this article, nothing extraordinarily perspective changing, but all of them interesting enough that they more than warrant an article of their own and most of them are tricks that most of us probably haven’t seen before.
For example, try these two option tricks on for size:
Option-click on the close tab icon in Safari, closes all other tabs. Handle this one with care – there’s no warning dialog.
Option-arrow moves cursor by word. One for the Windows switchers who are used to using ctrl-arrow.
I knew the second one; in fact I know several people who do a lot of document editing and writing who live by this tip, but I didn’t know it until I had to help one of them with their Mac!