The Expat Guide to Paris is a good place to start when researching your housing options in France.

Rental Market
For expats, Paris is often cited as the most desirable place to live in France. However, there are a plethora of wonderful options within the country. Note that Paris is also the most expensive places to live with rents decrease the further they are from a city center. Flats within Paris also tend to be quite small, even by European standards. A chambres de bonnes (servants's quarters) is a staple of inexpensive housing within the city and offer small, charming spaces with shared baths. One-fourth of the French population lives in housing subsidized by the government. Living conditions are below that of accommodations in the suburbs. Within the city there also exists modern, spacious apartments with impressive price tags.

Search Engines
Online search engines are one of the best ways to get an estimate of the current market and to track new properties. Most sites allow you to set-up alerts to find the best property for you. You can also list an ad for what you are searching for.

pap.fr
fusac.fr
Craigslist Paris
www.seloger.com - compilation of ads from real estate agencies
www.unnid.com/en/intro - housing search engine which aggregates results from various housing boards.
Another great online resource is the classified on EasyExpat.

An estate agent (agent immobilier) can be a vital tool for finding the right place quickly. A good agent knows the legal pitfalls and has access to a variety of housing. An agent will provide you with a description of available properties, escort you to viewings, make sure your contract complies with expected standards.

Anyone else have recommendations or advice?