I have been using Jigsaw for sourcing for the last 3 years and find it useful. Jigsaw is a large database with contact and company information.
They have over 10 million contacts in Jigsaw. For every contact you will get first, last name, title, email, phone, and location. Since this DB of contacts is created by Jigsaw users, there are many contacts that are wrong or obsolete (in my experience, on average, half of the contacts I get have errors). Still this is a very good source of information. I combine Jigsaw and LinkedIn to get cleaner and more up-to-date data.
Best of all, Jigsaw has recently made the company data free for all. You can look up company email patterns.
They have also introduced a feature called "company wiki" where you can read about companies. I haven't looked there much and would be interested to hear from someone who has.
Jigsaw is often confused with social networks; it's
not one of them. The question "Are you in Jigsaw?" they ask means that your contact may already be in their database - take a look.
You can join here:
http://www.jigsaw.com/join/freetrial
(Here's my full disclosure: if you join through this link I will get 125 "points"; 5 points is the "price" of one contact.)
Jigsaw offers a free and a paid option. I use a free account. To use Jigsaw and keep your account free you would need to add or correct the existing data. Or, you could choose to pay for their data, it's up to you. They won't switch you unless you select the paid option.