Here are some questions typically people ask consultancies/companies before choosing one.
This is my compilation, hope it helps.
1.How can you rely on this consultancy, did you have any friends working/worked with them? How did you knew about this consultancy, how much you can trust the source itself?
2.Is the consultancy capable of marketing you?
3.How much fee they charge you for processing your petition, as per law they are not supposed to take any fee, but many consultancies do charge with a valid reason – what if I apply for your visa and you do not join us?
4.What will be the mode of payment?
5.If they charge any fee, when are they going to return that back? (Usually consultancies give the money back in a year or so, if in case you transfer your H1 before that, you end up loosing that money, but it would be worth to do so based on the situations)
6.What is the number of H1 rejects/approvals in the past, a little bit of history?
7.What package can you expect for your current skill set?
8.How many clients/projects the consultancy has got for your skills?
9.Is there is any bond or fixed period you are supposed to work for them?
10.Does the consultancy requires any original documents of yours?
11.What options do they have for you? Fulltime or hourly rate? Each consultancy/company have their own policies, just try to get an understanding which will work best for you.
12.When do they expect you to come to US? (if you get your H1 approved)
13.What are the other benefits the consultancy has got? Example profit sharing/bonus etc.
14.Will the company pay for relocation allowances during projects?
15.Will the consultancy process your Green card?
16.Who will bear the flight expenses?
17.What kind off accommodation and allowances they will provide you?
18.When will you be covered by insurance?
19.Will there be any bench period salary?
20.Do they want you to do any certifications? As part of improving your technical expertise.
There are lots of Yahoo/google groups where you can register and get to know about various consultancies/companies.