tips for finding Paris apartment for several years

can anyone suggest a good website for looking at Paris apartment rentals, or could you recommend any agencies that help with long-term rentals there? My employer is paying but I have to find the apartment myself, and so far, even with a pretty big budget, other than Se Loger and Craigslist Paris, haven't had a lot of luck searching Paris apartment websites (lots of websites seem to be for studios or holiday rentals, but I need a family-sized central Paris apartment for at least 3 years...)