There's no one single bluetooth that's made specifically for the Droid X. Being that there are literally hundreds of make/model of bluetooth devices to choose from, it really boils down to what your preference is. What style and brand you prefer. And what features are most important to you. ie: noise cancellation, etc. I've got a Motorola H500 that I've used for the past 4 years and it works great. I've used it on my last 3-4 cell phones and am currently using it on my Samsung Fascinate. They've discontinued the H500 and replaced it with the H850 I think it is, but I do know Motorola makes some great Bluetooth earpieces that both look good and function well. It's all a matter of preference really.
Good luck...I'd like to see what others use/suggest as well.