Considering how big of a South Park fan I am, I'm really surprised this is my first list about the show.  Check out my top 5 list of secondary(not main, one-off, or obscure) characters from South Park, Colorado.

Number Five: Jimmy Valmer

Jimmy Valmer is a wise-cracking, "handicapable" student at South Park Elementary, voiced by Trey Parker.  Jimmy is an active stand up comedian and holds several records in the Special Olympics, even though he used steroids to achieve at such a high level.  His first appearance was in season five during the episode 'Cripple Fight'.

Number Four: Towelie

Everybody's favorite stoner, Towelie is a talking "RG-400 Smart Towel".  Towelie is concerned with two things in life, making sure everyone remembers to bring a towel and smoking weed.  Towelie's drug addiction got worse in time, getting so bad that the boys had to have an intervention when the towel was smoking meth and doing heroin.  Towelie is voiced by Vernon Chatman and was originally created as a joke about the over marketing of the show.  Both Towelie and Cartman consider Towelie one of the worst characters ever.  I was actually Towelie for Halloween a few years ago, and it was the easiest costume ever.

Number 3: Mr./Mrs. Garrison

Mr. or Mrs. Garrison is the teacher of the boys and one of the most complex characters on the show.  Voiced by Trey Parker, Mr. Garrison will have sex with pretty much anyone or anything and has undergone numerous sex change operations, but remains one of the most bigoted and intolerant characters in the series.  Garrison has had two imaginary teaching assistants, Mr. Hat and Mr. Twig and a real gay love slave, Mr. Slave.

Number Two: Randy Marsh

Randy Marsh is the father of Stan and Shelly and husband of Sharon.  Randy is based on Trey Parker's father and voiced by Parker himself.  Randy is quick to overreact and jumps on any idea, bandwagon or thought that comes his way, regardless of truth or practicality.  Randy loves to party, is a known liberal and generally is a pretty good father and husband.  He also has laid the biggest turd ever.

Number One: Butters Stotch

Butters is a classmate of the boys and easily one of the funniest characters on the show.  He's voiced by Matt Stone and is naive to a fault.  Butters is always trying to be a good kid, regardless of what life throws at him.  He gets stressed often, worrying about what his parents will do if he gets caught misbehaving, rarely curses (Oh, Hamburgers!) and is pretty much as wholesome as a glass of milk.  Butters does have a dark side, known as 'Professor Chaos' and has been the featured character in many episodes.

Source: South Park Studios
Source: Wikipedia