Do you use Salesforce? You may want to check out these two useful tools.
The first is DemandTools, a standalone application for manipulating data and administrating your Salesforce account. DemandTools features 14 modules, but one of its more popular features is probably its extensive deduping capabilities. It has certainly made this usually repetitive task much less time consuming for me. DemandTools also has the ability to verify addresses through a third party. It's not free, but comes with 450 free "credits" per Salesforce login.
DemandTools has many more features, but it's not overwhelming. CRMfusion, the author of the application, has very neatly documented all the features on its website, including mini-presentations of how each feature works.
The second tool is the Apex Data Loader, created in-house at Salesforce to import data. I recently used it to bulk assign contact roles to a large set of opportunities in order to run a report of opportunities with contacts from accounts.
In order to test out Apex Data Loader, log into your Salesforce.com account, click Setup, Data Management, AppExchange, Data Loader, and then Download.
Also, thanks to the folks on the Nonprofit Salesforce Practitioners mailing list for bringing these useful tools to my attention.