Once I compile a list of companies, I go to Hoover's
to find out more about them and their financials. A Hoover's subscription is a small price to pay to know more about a company and the major contacts within the company. After all, you do not want to deal with losers.
I don't mean to steal anyone's thunder here - its not my thread - anyways, I've used Hoover's and other methodologies for the same (and similar) purposes, and I have some added tips on finding relevant contacts within a company:
Press Releases - Many press releases contain quotes from managers and such within a company. Find a press release announcing a new product in the same field as yours, and you will often find the name of a relevant contact (and their exact title).
Annual Reports - A company's annual report is often made available somewhere on its website in PDF format. These reports will not only include detailed financials, but many will also include a page listing anywhere between 5 and 50 executive/manager names and titles.
Reference USA - This database will allow you to search for companies and it will provide full contact info along with executive names and annual sales. I'm not sure that the executive listings will be as solid as those provided by Hoovers, but this database can often be accessed for free through a public library, and results can also be extracted into spreadsheet format 10-25 companies at a time if desired.
Dunn&Bradstreet's Selectory Database - This is the best business database out there. Its extensive, you can fully customize search criteria, it is a good source of contact names (as good or better than Hoovers), and search results can be extracted into a spreadsheet 100 at a time. Thats said I'm pretty sure its more expensive than Hoovers.