Very often, this depends on our deployment platform and/or our client's environment. If we can, we'll look at open source tools and deployment options first with web or java front-ends and MySQL/Postgres databases, otherwise we'll go down the proprietary road.

From a developers's perspective, most of the time we like to use open source tools Eclipse and all the amazing plugins for our Java development effort.Otherwise, we'll use the Microsoft development suite Visual Studio.

 Some of the languages we develop in  include PHP, ASP, c#, VB, Ruby

More recently some of our developers have been using Aptana for Ruby on Rails development, it's a personal choice however.