The ambiance differs dramatically depending on where you're located in Miami; however there's something for everyone.
The downtown financial district on Brickhell Avenue is a cosmopolitian melange of large companies, bank headquarters and luxury high rise condominiums and penthouses. South Beach houses the famous Art Déco District, an attraction for the "branché" crowd and is also well know for its night life. Bal Habor, north of Downtown, is a chic residential community with luxury boutiques as is Sunny Isles with its new ultramodern buildings on the water nestled between immense commercial spaces along Collins Aveneu and are both favourites of the international population. Aventura is a chic residential area known for its world famous Aventura Mall, ranking as one of the top five highest grossing malls in the country in sales per square foot. Mediterranean style gardened villas comprise the landscape of Key Biscayne, Coconut Grove and Coral Gables located south of downtown Miami and draw the attention of multinationals and liberal professionals.
Consult http://miami.craigslist.org or http://miami.backpage.com for further information on real-estate.
Other addresses for roommates are:
http://www.roommateclick.com
http://www.roommates.com
http://miami.metroroommates.com