Many Mac users are already familiar with Growl. This software gives you notifications for things that happen on your PC. When a friend comes online, a new email is received, a file download finishes or the now-playing song changes in iTunes, Growl will tell you. You can also choose where Growl pops up to notify you, unlike a lot of the other notification pop-ups (or "digital toast") we have to deal with. The Windows version doesn't have quite the polish of the Mac version, but it's a good start.