Spent ages today (and over the last few weeks) ear training. Major and minor triads, augmented and diminished. Singing scales (major, natural minor, pentatonic and blues). Seventh chords, rythmns. It has been a lot to take on board. The best free resource seems to www.teoria.com.
For singing scales I have also been doing this with a keyboard - singing first and checking. Its amazing that if you don't practice for a few days (because you are busy on something else) its easy to forget. So regular practice is important! I have found recognition of the chords difficult.
Although I play be ear I have not had formal aural training in the past and so this is a steep learning curve for me. I have been taking it small steps limiting to two types of chord at a time and trying to work out strategies to differentiate them.
Listening for the thirds and fifths is important. I am improving but I find that after I've been doing it for a long time I start to get worse again. Why is that? Too tired? Ear gets confused because by the end of the session you have done so many? Hey ho.