AppBrain - the guys who are constantly innovating how you can use the Android Market away from your phone - just pushed an update to their Android app. The app will essentially allow you to install applications that you find in the market from AppBrain at the click (or a few clicks, in some cases) of a mouse button.
They're calling the feature Fast Web Installer and it's a separate add-on you'll need to download from the market alongside the main AppBrain app. For installation and usage instructions, refer to AppBrain's site (note: you'll need to give AppBrain and FastWeb Installer permissions to use your Google account and install apps over the air this way). I've played around with it and it's actually really simple. You find an app using AppBrain that you want to install, you give it permission to install the app, and then it pops up almost instantaneously (just like Vic Gundotra showed us at Google I/O).
I haven't checked out the feature with a paid app (no, I have not yet taken the paid app pledge. Sorry.), but our friend Andrew Kameka at Androinica notes that only free apps are able to be installed with minimal clicks as I've described above. I'm guessing this is a security measure, but no light's been shed on that by AppBrain themselves. If you want to try it out, you can find AppBrain Market Sync and the Fast Web Installer in the market today.