I am working at a startup software company in the SF Bay Area.  We are
interested in fining professional recruiters to help us find, attract,
and hire excellent software developers.

There seem to be many recruiters available, but I'd like to take a
stab at finding the top 5 or 10 firms, in the SF Bay Area, who are
especially good at finding and placing very skilled software
engineers.

Does anyone know how to do the research to propose 5-10 of the very
best recruiters in the Bay Area to focus on?  I'm NOT looking for
random, unranked firms (I know plenty of random firms).  I'm looking
for some evidence that suggests the firms are likely to be noteworthy,
effective, high-quality.

Anyone have some ides for 5-10 exceptional software engineering
recruiters in SF Bay Area?

I would like to know what services do you expect the recruiting firms
do for you and how do you define their quality of services.

Here in HK, I always feel the recruiting agents are doing nothing
except getting some commissions (which I think it's completely wasting
of money).

What they usually do here for the clients are:
1. Read some CVs
2. Call the candidates and ask whether they're interested in the openings
3. Arrangement the meeting with the Employer
4. If the Employer is ok after interviewing, tell the candidate
5. Get commission and done the deal

What's the value of their service? I really don't understand why so
many companies like yours are using recruiting agents.

The primary functions I expect the recruiting firms to do:

1. Gather the CVs from all sources (boards, contacts, universities)
2. Accurately filter the CVs for particular role requirements
3. Provide high-quality CVs to the firm

The other administrative functions are helpful but not distinctive.