Android/Chrome: Google's Cloud Print setup is a little rough around the edges right now, but the possibilities are looking nice. An Android app, for example, uses Dropbox and Cloud Print to fling almost anything you see or open on your Android over to your (Windows-connected) printer.
You'll need to get Cloud Print set up on Chrome, loaded with Windows drivers, to print directly to your printer. But Cloud Print Beta for Android also uses Dropbox to stash the files you want to send over, so you can print them the next time your printer is connected. You can send files directly from the app, or use the Share function with other apps to send them over. I've managed to print a test page and a DOC file from my Android to an HP printer, connected to a Windows 7 computer so far, while printing an image from the Gallery seemed to glitch out.
Google's own webapps also allow Cloud Print-ing from Android. For everything else, Cloud Print BETA might fill in the gaps. It's a free download for Android. Thanks for the tip Paulo!
Cloud Print BETA [Android Market]