The hardest I ever tripped on mushrooms (about 4.1 g's; not my highest dose but certainly the strongest) I had a few pretty crazy hallucinations. As I started peaking the first visual I noticed was a rainbow ethereal liquidy film slowing enveloping the floor, walls, and ceiling.
Shortly after my friends welcome mat began morphing into anything from assorted swinging medieval swords, all the components of a Swiss army knife, writhing worms and snakes, etc.
The coolest visuals in the trip would have to be a tie between what his shag carpeting would turn into. At one point I remember the carpet turning into infinite tiny replicas of a suburban street with a few houses, cars, people, and a church, all identical and right next to each other extending as far as the carpet went.
At another point on the same carpet, large multicolored ziggurats appeared to rise out of the ground and as soon as they would reach their highest point, thousands of flies would appear and swarm around it. As the ziggurats receded back into the ground the flies would systematically disappear in a very mechanical and clockwork-like fashion.