1. MSBuild or NAnt
   Build automation tools by which a developers can use XML scripts to automate all the hassle tasks of creating a build: retrieving code from the source control (SC), labeling the source code, building it, zipping it, emailing info, and many other tasks. Both tools are free.
2. CruiseControl or TeamCity
   Continuous Integration servers that utilize the build automation tools to add extra slick functionalities like monitoring the SC, issuing specific commands on specific actions done on the SC. CruiseControl is free while TeamCity is not.
   I once heard a really interesting utilization of such servers; the dev team had red and green bulbs placed in a noticeable area where everybody could see them. On each code check-in action the servers would initiate a build on the server, so if the code builds successfully the green bulb would light up, if the build fails the red bulb lights up instead. nice ha!
3. Tarantino
   I still haven’t got the chance to work on this tool, but it says it does the thing I really wish more companies start to embrace; which is having a separate database instance for each developer instead of shared databases.
   This tool would let the database changes to be incorporated into the SC as easy as code check-in’s (including Schema changes). So in any instance of time, the developer will be able to get latest version of code and sequence of scripts and work on clean ready environment where code and database schema is 100% compatible.
4. RedGate Sql Compare
   It enables you to compare two database instances and to elicit a change script from this comparison. One of the many features, by which it supersedes its free counter part SQLCompare, is that it can be initiated from Command Prompt. costs at least $390.
5. TortoiseSVN
   SVN(SubVersion) is an open source SC. TortiseSVN is an SVN client that integrates with the Windows shell. Lovely, robust and free.
6. AnkhSVN
   it’s an SVN client too, but integrates with Visual Studio so you don’t have to leave the IDE to manage versions, indispensable. It’s free.
7. TFS sidekicks
   if you have ever dealt with TFS administration, you’d know how cumbersome it is. TFS SideKicks is the solutions, period!
8. NUnit or xUnit
   For the ones who haven’t heard of Unit Testing tools (I hope you are few!), you will be able to write code to test your code; and with nice GUI which tells which part of your code fails. Both are free.
9. IE8 Developers tools, Firebug for Firefox
   These are awesome client side environment tools; Debug Javascript, Profile Javascript, and manipulate CSS on the fly. web devs can’t live without it really. both are free.
10. Fiddler
    inspects http requests made from your browser, with details to the smallest bit came into your machine through http. It’s free
11. WinMerge
    The best diff tool out there, I wish I could replace it with every IDE Source Control plugins, it compares folders too. It’s free.
12. BugTracker.Net
    If you have a small team of devs who work on low cost and tight budget project where you can’t use Jira? this is THE bug tracker software I choose. I love their new feature integrating with SVN. And it’s free.
13. DPack
    Code navigation tool; light, handy, free.
14. CodeRush or Resharper
    code assistant and enhancement tools, makes you create, change, refactor code in couple of key strokes. They are both not free except CodeRush has an Xpress version

I am sure there are others slipped out of my mind, but I believe those are fun enough to play around with. enjoy