I don't know of any agencies, but http://jobs.chinwag.com/ always has a lot of vacancies, and you can register for their email list.

For recruitment agencies, specialists are best. You will find agencies that specialise in Engineering, accountancy, law, etc. These are always better for specific industrial or service industry placements. Avoid general agencies which do typists to chefs, warehouse men to fork lift truck drivers. So when you search, try putting the field you are working in in the search criteria as well.