3rd Party Application to Find missing lead info in SFDC

Hi

I am sure the problem I am putting here is not unique to me but lot of other marketers must be facing this. I have lot of lead in my database where the information is either missing. Are there any third party tools which can get me this missing information( I am using Data.com and it not very helpful)? Are there any alternate approach to keep the data clean in SFDC? 

Thanks