Both - I have a network of recruiters that I stay in contact. They know what type of work and rate I am looking for and roughly the overall time frame when I will be coming on the market. Most usually check in monthly just in case something has upset an apple cart.
I also pay attention for listings within 1 month of expected end of a contract.
DICE/CareerBulder/Monster are the three main job sites that I utilize.
Many recruiters will also have their own listings; however, I prefer not to go looking for 10-12 sites every two/tree times a week. They have my papers - it is up to them to determine potential matches.
The real frustration is those that either can not read the job descriptions or the resume and essentially spam you.