Other
Big Ears: The Original Online Ear Trainer
This is an excellent resource to help you identify intervals. You can choose which intervals you would like to hear and it will play them for you. You can also play intervals on the virtual piano and it will tell you what they are.
Other
Functional Ear Trainer
This is a freeware software product that can help you develop your ear training. There is a basic and an advanced version of the program.
OpenStax
Open Stax: Catherine Schmidt Jones: Ear Training
A detailed site explaining about ear training for musicians. Included are many links to other relevant articles that go more in depth about the various aspects of developing ear training. There is also a downloadable ear training game to...