We've acquired contacts from a variety of the usual suspects over the years: RainKing, DiscoverOrg, Jigsaw/Data.com, etc. etc. They each have their own profile data of the type we're specifically looking for (revenue and number of employees; industry SAIC number and such are easier to acquire). We currently use ReachForce for data append both for leads and accounts. But as we're finalizing our ideal customer profile, we're aiming to choose a "vendor of first recourse" for account profiles (we'll address contact acquisition later, after finishing our ICP). That is, we want our baseline to at least start from a single, consistent source. We may get better data directly from the prospect account or some other source, but we at least want all departments to agree on the starting point, rather than picking and choosing opportunistically from our plethora of sources that are often inconsistent or suspicious-looking. Recommendations on vendors? I'm focusing first on the best fit to our business needs, not on technical integration capabilities. We want to stack rank the best sources first, and only then sift through technical requirements. Naturally, Dun & Bradstreet is appealing. Alternatives? (That aren't focused on credit reporting.) We are not considering vendors that provide "socially acquired" data ranges of the type you get from LinkedIn or similar sources; we have found the data ranges from "just OK" to "obviously wrong" to "bizarre.") Thanks!
We use InsideView and are happy with it. They do some social crawling to get data, but also get it from other sources as well.
They consistently rank very high in both data quality and user satisfaction. Price tag can be steep though.