#1
I've been playing for about 3 and a half years now and feel I neglected ear training. I wanna get started on it cuz it's an invaluable thing to be able to do. I need some suggestions as to what songs would be a good starting place. I'm into lots of classic rock and modern rock and blues.
#2
Any song would be good to start. It doesn't matter which one you pick.

There are various methods for ear training:

Identifying major and minor chords by ear.
Listening to a note, then waiting 10 seconds and locating it on the guitar.
Listening to a note, then waiting 30 seconds and locating it on the guitar.
Listening to a note, then waiting a minute and locating it on the guitar. You get the idea.
Listening to a rhythm and either tapping it out or playing it after several seconds. Use the same concept as above.

Get the idea?
#3
Start with pretty simple stuff. Learn some pop songs by ear. Start with the melody, then try to work out the chord progression based on the notes used. It's gonna be tedious for a while. Definitely start with something that has relatively good recording quality (no black metal!) and sounds simple in terms of melody and rhythm.