I'd say my best friend is my brother. We've been through everything together, have a basically identical sense of humor, moral code, and view of the world. We had our issues growing up (what siblings don't?), but he's always there when I need him and I try to do the same for him. He's always able to make me crack a smile, even when I'm fighting not to. He still makes me crazy sometimes, and I'm sure I do the same to him, but that's just part of life.
Too many memories to list them all but I think my favorite was he and I went on a trip together when he graduated high school down to Jamaica. We really bonded, though a lot of the memory of that trip is, ahem, hazy to say the least