It's not Wi-Fi per se, but you can use the app AwesomeDrop for one way transferring from PC to the phone. You just drag the files on your PC to your browser. Then on your phone load up Awesome Drop and they're all there for download.
It's quick and easy but only one way. I personally don't use it that much since I primarily use Dropbox.
I wholeheartedly and emphatically suggest WebSharing from android.nextapp.com (available in Market for $2.99). I've used it on a VZW Droid Inc and a Tmo Vibrant and transferred over 2GB across hundreds of files at once. Worked wonderfully. Took a minute to get used to the interface and after that zoom zoom. I have not tried the WebDAV support yet. -Pk