Ear Training
Ear Training - Dylan Baker Music
Pitch recognition is one of the most valuable skills a musician can have. Although it requires extra discipline and effort to perfect, the results are extremely worthwhile.
Ear training will better allow you to perfect your own playing in being able to correctly distinguish your notes and rhythms, and it will allow you to play with other musicians in a more advanced manner.
The above website is my personal favorite and one that I've used for years. I still visit the page as often as I can to fine tune my own ear training abilities.