<human>: Condense the text into a few key points

This is [Buddy.] I adopted this 60 lb mutt (German Shepherd and Husky are evident, but there's gotta be other stuff in there) from the Richmond SPCA in September 2009.  He was 10 months old then and was instantly a great dog.  He never chewed anything or had a single accident.  

The only behavioral problem I've had with Buddy is that he is very excited when outside on a leash, constantly pulling and never looking back.  I've been able to correct the behavior with training and a [Gentle Leader] to the point where he is usually on a loose leash and even off-leash when I know there will be few distractions.  Unfortunately, he still gets really excited around other dogs and some random people and pulls at the leash and then gets upset and barks when he can't get to them.  He is extremely friendly and playful and has never bitten anyone or anything.  I had hoped the gentle leader would fix this, but instead it just causes his head to jerk around when he lunges and then he fights the collar and looks like and ABSOLUTE psycho, scaring people all around.  I just want him to be able to ignore these distractions unless I allow him to interact.  He is a very smart dog and I'm certain he could learn if I knew the correct way to train him, which brings me here!  So...any suggestions?
<bot>: dog usually walks well on a leash until there is another dog or bicyclist nearby which causes him to flip out when he can't reach them. need help.