I voted for:

.405;
.50/110;

and will vote for .303 British as well.

How do you vote more than once? I had to wait a long time for the cookie to expire before the second vote.

A .375 and .300 Flanged would also be cool. I also thought about the .450/400's.

As for the .577 T-rex it just shows how many dickheads vote in these things and how unreliable some of the results are. The boring .30-06. .30-30 and .45/70 lead the list of course.