I know they now have external wifi drive and drive enclosures and they now have wireless USB. But do they sell a simple dongle that can be plugged into a usb device and maybe with a little driver support be able to control the USB device via wifi?

I was thinking about getting a 3.5" HardDrive media player (HDD enclosure, that can play movies and music stored on drive) and it would be nice if I could mount that into my AV rack and load movies/music onto it without having to connect a USB cable each time. Kinda like a WiFi to USB dongle I could plug in the back, then setup my system to view the media player as a drive, then it's just drag and drop from there.

I don't think they make those.
You could possibly pair a wireless media player up with one of those stand alone home network servers.

Well what I was thing (now I that I looked at it) my wireless router has a USB port for a USB external drive so you can have a network storage system. So my case could work. However my friend who is getting the same thing does not have a router. So he might have to find something else. He could get a wireless USB hub, but then he has to have a USB dongle coming out of his laptop. I know his laptop has wifi built in, so I was trying to find a way to use that.