Coworking is a growing concept for shared office space, particularly suitable for web workers, contractors, and independents. Some charge by the hour, some charge by monthly rent.

Google Group for coworking - arguably the best place for leads / discussions about coworking

Coworking wiki - arguably the most comprehensive wiki about coworking - Coworking community blog

Where you can cowork [this is an incomplete selected list of cowork locations I've found]: - Jelly = casual coworking, sorta like a meetup but to work in proximity with others

For longer-term commitments and a permanent office space, good options include HQ and Regus. This is great for when you don't need a whole office building, and want an office space for 1 to 5 people.