I'm already showing signs of getting referral spammers, and I get hardly any traffic and have no visible referer logs other than my log analyzer, which is in turn covered under robots.txt. Fortunately, a number of people have come up with useful techniques to cut down on the flow, and I'll be linking to the best of them below. Unfortunately, the solutions fall into one of three categories: whack-a-mole spammer mod_rewrite entries, blacklists with unclear formats and maintenance standards (some specific to MovableType, though using mod_access to make use of existing e-mail blacklists is an interesting idea), and dangerous pattern matching.

Well, the first is safe enough, if somewhat burdensome. My own mod_rewrite list excerpted from my Apache configs is here, and the best of the referrer spam guides is listed below, sorted by blog name.

Ann Elisabeth, who's entire blog seems to have been temporarily diverted to the purpose of running down spammers of various types, though she does have one entry in particular devoted to referral spammers.
Caveat Lector
ILoveJackDaniels
jessey.net (who has posted her own Apache config)
Tom Sherman (Jotsheet), with a guide to blacklists
Visual Intensity, which specializes in the adminshop spam.