The vesper bats series. The first (and so far only) long Tet Zoo series (20 parts!) to actually be completed, and in roughly just a single month at that. And yes, it covers every extant species of vesper bat.
The entire blog itself for zoology blogs.
Naish's identifications of several strange animal carcasses widely sensationalized as "monsters" in the media. Revealing the "Montauk Monster" as a raccoon carcass might be the best (and most famous) example.
Covering the obscure snakeBothrolycus ater, just to see exactly how much can be said about such an obscure species. Yes, we still get a lengthy, informative post.
Showing us that rabbits of all things are "the freakiest of all mammals".
Discussing cryptozoology in a scientific manner, instead of the stereotypical pseudoscientific junk practiced by many self-proclaimed cryptozoologists.
The very first post (with actual content) and you just know that this blog is something special.
Steve Bodio (first commenter on said post): First, this is without a doubt one of the best blogs ever— I'll put it on my blogroll immediately.
The fact that, even with schedule slips, Tet Zoo has been updated at a fairly regular pace over the years, something that many other otherwise excellent science blogs haven't been able to manage.