One happened during my junior year. I lived in a house with two other guys, who were out of town for the night, so I was home alone. I was short on cash so decided to just stay home, and I was playing guitar out on the stoop of my house drinking from a bottle of cheap wine that was left over in the fridge. I was pretty delighted when two drunk guys threw a fiver on my porch as they passed by - I was definitely not playing to any level that deserved money, but it felt pretty awesome.
An older hippie looking guy came stumbling down the walk. He stopped and asked me if he could play something on my guitar. I was immediately nervous that the guy might run off with the guitar, but I hesitantly handed it over to him, and he strummed out a song which I had never heard before (Bob Dylan's She Belongs to Me). He was no rock star - his chord changes were sloppy, his voice was raspy and maybe a little off key. But he shared a wonderful song that I love to this day, then thanked me for letting him play and continued on his way. What a cool little moment, to meet this random stranger and be able to share that music.
The other moment was even more strange and magical, and happened about a year before. A buddy and I had been holed up in the house watching TV and smoking pot for a while, and we stepped out onto the stoop to have a cigarette. It was a beautiful spring afternoon, and we were just chatting, goofing around with accents and silly jokes, enjoying the fresh air and the leftovers of our weed high. All of sudden we heard this strange, ethereal music coming from down the street, and went silent as we strained to hear the sound. From the street corner emerged a man in a forest green suit, with a long white beard, carrying some sort of harp, and playing it beautifully as he walked by. The guy didn't acknowledge us in any way, and we were far too shocked to think of anything to say as he passed. We watched him walk away, still playing this almost angelic music, and the music faded as he got out of hearing distance. My friend and I stood there in stunned silence, until one of us asked, unbelievingly "did you see that too?" I never saw this guy on campus again after that day, but my friend and I still joke about the time we saw an actual wizard on campus. If I hadn't had a friend with me, I'm not sure I would believe that it was real, I'd chalk it up to some vivid dream or hallucination or something. But again, what a magical thing to have happen.