That's advice most people would expect to pay for. Nonetheless, I'll try to come up with a few for you. Bear in mind that I'm going to have to get REALLY creative to come up with some that aren't taken.
WebmastersoftheWorldUnite.com
WebmastersGetTogetherYeahYeah.com
WebmastersForJesus.com (if you want to get in a niche).
WebmastersForSatan.com (if you want to get in a different niche).
TransgenderWebmasters.com
HolyJumpingUpAndDownHairyWebmasters.biz.
Feel free to use any. Don't be surprised if I call in a favor, once you get rich from your webmaster forum.