Ricci Adams' Musictheory.net offers an online trainer to help test interval recognition. Interval recognition is the first step towards harmonic awareness.The trainer plays a series of intervals and the listener must identify the intervals based on the notes they heard. The trainer offers feedback on the right or wrong answers. The trainer also allows the user to modify which intervals are played so that he/she can focus on a particular set of intervals.
Good Ear offers an Interval ear trainer designed for a beginner that focuses on a small range of intervals. It also has a variety of trainers that focus on different aspects of ear training including chord recognition. Good ear offers a pitch trainer for anyone that is trying to train themselves to have perfect pitch (naming each note by ear).
There are a variety of virtual pianos that you can find online by googling "virtual piano" or by clicking the link in "Resources" below. Virtual pianos offer a more advanced level of ear training. The more advanced musician can focus on their own personal weaknesses by playing them on a virtual keyboard. Virtual keyboards allow the musician to play, see and hear chords, intervals and pitches at their own pace. Using a virtual keyboard also helps to strengthen piano skills which can be applicable when assisting others in group ear training sessions.