I recently participated in a "Top 10" ranking poll for FightTicker.com. As a member of the ranking team, I submitted my Top 10 fighters in each weight class from Heavyweight (206-265) down to Featherweight (136-145).
You can find the final lists on FightTicker here. These are really for FightTicker.com purposes more than anything else. We're not saying that our rankings are better than any other website's (even though they are). We just use them as a more official way to speak of the fighters we're writing about (i.e. "FightTicker's #1 ranked Heavyweight Fedor Emelianenko decided today that.....").
Members of FightTicker do these rankings approximately once every quarter, so the next rankings will be published in February. If you're interested in getting in on the next rankings, head over to FightTicker and join the site. The spots on the rankings team are open to all members of the website.