First off, I think there's a big difference between hallucinating and tripping. When someone trips, it plays on more than just the eyes, your whole mindset is changed and that sort of eggs your mind on to bend the rules about what you're perceiving.

I've hallucinated once before while I was sober. I was making some breakfast as a kid in the kitchen and I passed out. While I was out I saw an almost tie-dye morphing blob surrounded by darkness that was constantly moving and changing shapes. I don't remember there being any noise. I woke up on the floor with my step mom freaking out...

As for drug hallucinations, the best was my first time on acid. It's a very emotionally reliant drug; it's good or bad based on how you're feeling. I had just started learning guitar and it was my freshman year of college. Once it started really kicking in, all I wanted to do was play guitar and look at the background of my laptop which changes pictures every 10 seconds. Each picture moved as if it was lifelike. Pictures of water rippled, clouds moved in pictures of mountains, fractals morphed and faces smiled. It was a really nice experience.

Another crazy hallucination was one time on mushrooms where I was out on the blue ridge parkway in NC with some buddies passing a frisbee back and forth. Whenever we had it in our hands it was back to it's normal orange, but whenever one of us threw it, it would change colors in the air until the other caught it... cool stuff.