Tate Britain: Tate Molluscan
More infested in large.
Alternative: Martin Creed Artist Room (more faith necessary?)
We (see if you can find Im) went to see Monster Chetwynd's slugs adorning the front of Tate Britain; I've passed by several times (en route home from St. James's Park) and kept thinking that they're probably worth a closer look (/explanation). One rests on the steps' parapet, one climbs a column, and they've left their mark on the whole façade with their electric slime...
I thought that they were rather amusing and livened up the place, although the rest of our sweep through the galleries left me seeing them as a form of false advertising really... As usual, I found the spaces and visitors much more appealing than most of the exhibits.
Others here (or right from Boat, building, and building buildings)