Our directory on the site here will let you search the most up-to-date listings for agents for tv and all other types of writing. Most charge 10% for UK representation, ie. 10% of what you earn they take. And usually 12- 15% on foreign monies. Nobody good will charge more than this.
Depends what for-- are you wanting the big literary ones, who are much more mainstream and need fast returns for their money- because good agents do actually invest in their clients- or a smaller, edgier agency who are a bit more prepared to take risks? and TV, or prose, or...?