A list of UK recruitment companies who have a tendency to send out scattergun spam to digital agencies, in a format for dropping into your GMail filters.
That's not a bad idea. I've not really had problems with recruiters tweeting at me but if you've got a list then feel free to add a file with them all in.
How about including Twitter usernames? Clients such as Echofon allow users to be blocked (although I'm not sure it it's possible to import a list).