Developer Console  A browser-based collection of tools you can use to create, debug, and test applications in your Salesforce organization.

Force.com IDE  Eclipse plugin for developing Force.com applications, providing source code editors, test execution tools, wizards, and integrated help.

Force.com Migration Tool  A Java/ANT-based command line utility for scripted deployment of application metadata.

Force.com Explorer  .NET-based tool for inspecting schema, and building and testing SOQL queries.

Jitterbit Data Loader for Salesforce  A free, third-party data migration tool that lets administrators automate the import and export of data between flat files, databases, and salesforce.com.

Dataloader.io  No download, free data loader for Salesforce. Leverage keyboard shortcuts for object lookups and data mapping. No security token required.

Informatica Cloud Data Loader  Informatica Cloud Data Loader for Salesforce is a FREE data loading application that automates the import/export of Salesforce and Force.com data between databases and files.