A few months ago I wrote about collective nouns for librarians in my Adventures in Library School blog.
Recently the topic came up on the knitlist about a collective noun for knitters. Some of the best ones were
a swatch of knitters
a purl of knitters
a skein of knitters
a row of knitters
I also found a list of collective nouns for various professions on Wikipedia . The linguist list also has a list which can be found here .
Another good source can be found here.