I got this, it was $5 after rebate. Works great with my WiiMote Motion Plus with Dolphin. Really, most adapters are fine, just check http://slickdeals.net/ for a deal.

The one I got: http://www.amazon.com/Asus-Mini-Bluetooth-Dongle-USB-BT211/dp/B0041UJVI2/ref=sr_1_2?s=electronics&ie=UTF8&qid=1388611607&sr=1-2&keywords=asus+bluetooth+adapter