Matty,

I'm assuming you are looking to buy a place rather than rent and that you are looking on the web rather than in Rome itself. You can google "immobiliare roma" and i think you will find some. Otherwise there are some national chains like tecnocasa which should google up OK. If you are in Rome itself you'll find that a lot of bars have a stand for agents booklets - the prices aren't often shown but sometimes they are and it'll give you an idea for area, prices and agencies.

Alternatively you could go along to the La Dolce Vita exhibition at Olympia, unfortunately you've missed this year's, but there are a lot of agencies there each year.

Hope that helps

David