Here's a good post, by Liz at the Social Networking Blog, about how to find contacts within specific companies.
A couple things I would add:
1) do not *ever* use just one search engine. Different engines deliver different results. Yeah, yeah, go ahead and use google if you must. Use MSN too, people.
2) Ditto with the whole yahoo groups thing. Forums exist all over. Don't limit yourself to just finding them on one site, search the whole web for forums.
3) Regarding searching blogs, I'd recommend technorati. Nothing against google, just that technorati is the de facto standard in my opinion.
4) "Press release", "press contact", "speaker bios"...all great keywords for searches (plus add something specific to your space)
5) Professional associations can be hit and miss. I often find that people working at smaller companies join more than folks at larger companies. It's about the time investment relative to the return. If your target is a larger company, you may have to look elsewhere.
6) My own little tip (shhh, don't tell anyone) is to go to the company website and use the following search logic (assuming the name of the company is "XYZ"). In their search box (if they don't have one, use the "search this page" function in your search engine): type "joined XYZ". Not every employee bio is going to have the work "bio" on it, but you'd be surprised how many have a line about when so-and-so "joined XYZ".
7) Search Amazon or Borders for book reviews/authors using the company name as a key word.
8) If the company is local, go where their employees hang out. This may sound a little stalkerish but if I wanted to meet a Microsoft employee, I could certainly tell you exactly where they hang out (Marymoor, ProClub, Sapporo Terriyaki at lunch, etc.) and I could also tell you how to spot them (parking tags). Yikes, please don't use this with me ; )
9) Go to the company job site and observe their job naming convention (for example, do they use "product manager" or "product marketing manager"?). Use that as a search term to find articles or postings that mention someone with that title.
10) Don't forget to ask your friends and neighbors who they know. The internet enhances relationships, it doens't take the place of them.
Anyone else have tips to add that haven't already been mentioned in Liz's post or here?