Data.com

I like the way Data.com clean allows us to essentially fill in blanks we have in our contact and account data. This allows us to have fewer fields for prospects to complete when submitting a form. We can get account firmographic data and it allows us to build a complete account profile. In addition, we can expand the number of contacts under the account and replace stale, older contacts with fresh contacts. It's easy to find contacts by sorting on industry and geography and we can drill down to the specific job function and titles we are looking for.

As is the case for any contact database, it's data is not always 100% accurate because of turnover. But given my experience with other contact lists, Data.com has been consistently more accurate. Another dislike: data.com doesn't allow you to snowball your monthly downloads. Meaning that if a user is allotted 300 downloads per month, but only uses half of those downloads, they can't use 450 downloads the following month.

Look at your needs and also the level of data you need. You also need to understand how accepting your users are of the data sources. Some users are not as comfortable with crowd sourced contacts as others and they are less likely to feel they are as valuable contacts as ones that are sourced through other methods.