What are some of the best ranking algorithms with inputs as up and down votes?
David MacIver had a nice post on the algorithm he used for ranking programming languages based on relative rankings from different users for various factors:
It's based the Rank Aggregation Methods for the Web paper by Dwork et al.
If you want something similar to this site, then Reddit's code is open source. There was some discussion of their ranking algorithm on Hacker News a while back:
For a quick and simple take on "hotness", consider Evan Miller's algorithm with time decay:
I have listed a number of schemes for solving this problem at Sorting answers, given overvotes and undervotes. I won't duplicate them here; just take a look over there. The most promising ones look like either Bayesian rating or Laplace smoothing.