CRMfusion - CRMfusion is a suite of data quality and data integration tools that integrate well with Salesforce.
Duplicate Check - Start creating data happiness. Find, merge and prevent duplicate records in your Salesforce Organization.
ImportBuddy - It gives you a very easy solution to Add/Update CSV data into any standard or custom object of Salesforce without leaving Salesforce.com
ZaapIT - Mass Merge, auto merge, duplicates cleanup, bulk edit, bulk update, bulk delete , mass lead convert
DataArchiva - The Next-Gen Data Management Platform for Salesforce
Cloudingo - Cloudingo - a cloud-based SaaS, connects to Salesforce and allows system administrators to scan their entire database for similar or duplicate records.