Many folks regard the Aliph Jawbone to be one of the best Bluetooth headsets on the planet. I tend to agree, which is why I'm excited that eCost is offering the Jawbone for just $29.99 (after a $6 mail-in rebate).
Alas, that rebate (PDF) doesn't quite cover eCost's ridiculous $9.50 shipping charge, but even the final price of $39.49 is well below what you'll find elsewhere.
Renowned for its fashionable design and unparalleled noise-canceling capabilities, the Jawbone earned an four-star rating from CNET.
Users were a bit less enthusiastic, mostly due to the awkward fit and difficulty pressing the buttons. I use a Jawbone myself and agree with the criticisms, but also think that once you've managed to wiggle the sucker onto your ear, there's no better headset in terms of audio quality.
I know eCost has a less-than-stellar reputation, but I've purchased from them many times without incident. (Actually, there was one incident, but they resolved it quickly.) If you want a top-rated Bluetooth headset on the cheap, this is the deal to beat.