I'm new to the site, and after reading many stories I thought I'd post my own. What I've experienced is neither as amazing nor as definable, but I think it's worth mentioning just to see if it sounds familiar.
I've had them as long as I can remember - short snapshot memories that hit me in the middle of the day. I use the word "memories" because that's what it feels like, but the important part? While these snapshots are too short to make out anything specific, I know they aren't my memories. An example: I was taking a history test last year (and being a history nerd, I was having a great time) when I got this image in my head, accompanied by a little snippet of sound and even some sensations. I saw two kids sitting on a back porch, playing with water balloons. A man stuck his head out of a window and said something. I was aware that it was hot and dry, like August in the South. For about two seconds I saw, and more importantly felt, this scene, and then it went away. I've actually had this particular snapshot multiple times; I always come out of it feeling a bit nostalgic. Other snapshots include a cat playing in front of a fireplace at Christmastime; something involving fog, but not in a creepy way; and walking around a farm on a sunny morning.
It may or may not be useful to mention that until this past summer, when I underwent surgery to remove it, I had a tumor on the back of my brain. Interestingly, I haven't had any snapshots since the surgery.
In addition to the miniature visions, I am also a number-guesser for lack of a better name. The first instance was in the second grade - my friends and I were reenacting Land Before Time on the playground, and two of us wanted to be Ducky. A third girl said, "Guess what number I'm thinking of, and the closest will get to be Ducky." I won, but the girl was a bad sport and called a rematch. I won again. And again. And again. I just heard the number in my mind. It wasn't a voice, but an unexplainable feeling. It still happens occasionally during guessing games. The weird thing is, it's only with numbers.
And unfortunately, it didn't keep me from failing high school math. ^_^