Monster is an incredibly combed website. Every company and it's subsidiary searches it. I was a tech recruiter for a couple of years and trust me, if you're on their and your resume fits the criteria, you'll be picked up and interviewed. Recruiting agencies have problems with double submissions when they use Monster - submitting a candidate to a company that's already been submitted by another agency.
Dice is a tad more exclusive, and you may get more serious interest from there.