I tried a couple of dlink USB wifi dongles and the TV didn't recognize them. I haven't read anything about any other compatible dongles. As an alternative, you can also use a wired to wireless (aka gaming) adapter in the ethenet port. If you have several wired devices near your screen (DVR, Blu-ray, Game, MediaPC, ...), you can hook them to a second access point configured as a wireless bridge to the rest of your network.
Here's an example of my network setup. We watched a HD movie streamed from Amazon last night. It worked great without a single glitch.
WAN(ISP) <--> Router / WAP1 <--> PC1, PC2, Printer
Wii (built in wireless connects to WAP1)
laptop (built in wireless connects to WAP1)
TV2 <--> Wireless Gaming Adapter (connects to WAP1)
Switch / WAP2 (wireless to wireless bridge to WAP1) <--> TV1, DVR, BD, PC, Xbox