Link straight to part of a YouTube clip: Instead of sending people to the beginning of a clip, you can create a link that plays from a spot in the middle that you choose. Just add #t=[number]m[number]s to the end of the URL, such as http://www.youtube.com/watch?v=Mf6IQgFxpIA#t=00m11s to begin 11 seconds in.
Initiate console game downloads: Microsoft's Xbox Live site might seem superfluous on a PC. However, you can queue up downloads and activate purchases through your computer, and when you log in back on the console, they'll transfer automatically.
Upload to Flickr through e-mail: Instead of manually uploading photos, you can send them through e-mail. This can work well from an old mobile phone to quickly send pictures from a PC. In the Emails & Notifications tab of the Account options, click Create an upload-to-flickr email address to configure the feature.
Search and link to iTunes content in a browser: The iTunes store lives in its own application, but you can access specific apps, songs, searches, or anything else with a URL. To search, try http://itunes.com/[search term] such as http://itunes.com/evernote. If your search comes up with a single result (as in this example), you'll jump to that page within iTunes. To copy a direct URL to an iTunes store page, right-click an item within iTunes, and choose Copy Link.
Feel free to share your own tips and tricks in the comments!