The two character spots I remember for the Fab 5 were Camp Minnie Mickey in AK, and the Epcot Character Spot (in Epcot, of course). We didn't have very long lines at Camp MM, which was nice, but you do have to wait for the characters separately, while at Epcot there is just one line to see all of them. We also got Chip & Dale, Thumper and Miss Bunny, and Pocahontas at Camp MM. These character spots appeared to run for most of the day.
The Disney Visa picture at Epcot is inside Innoventions West, I believe. It's the building with the fire truck. The Meet N Greet is only open from 1:30-4:30, and there are different characters each day, so you never know who you will see. We had Mickey and Pluto.
A lot of the World Showcase countries in Epcot have characters, too. Mulan in China, Aladdin and Jasmine in Morocco, Snow White in Germany, Belle and Beast in France, Marie in France, Donald in Mexico (in his Caballero outfit), etc. You can usually see at least 1 or 2 characters if you walk around the world. They do have set times that they come out, but it's not all day, so you have to check the guide or the signs in front of the countries.
The characters in DHS are a little more spread out. There are usually some characters in the central area near the Sorcerer Hat, then there's Woody and Buzz (and sometimes other TS characters) across from Midway Mania. Mike and Sully have their own spot near the Studio Backlot Tour. The permanent character spots are listed in the guide, along with times.
We didn't explore the character options at MK much, but I'm sure other people on the DIS have.
