Go Back in Time With Shadow Copies
This is one area where Microsoft was ahead of the game. The Shadow Copies feature built into Vista saves previous versions of your files, so you can easily recover deleted files or roll back unintended edits with a simple right-click. Shadow Copies don't require a separate drive, so they don't qualify as full backups, but they are incredibly useful. Unfortunately, few people know about the feature because Microsoft includes it only with the Ultimate, Business, and Enterprise editions of Vista, and because its bare-bones interface doesn't emphasize the feature nearly as well as Time Machine's.