Ken Miller taught my intro biology course. He’s not only my hero but he was a great lecturer. I get really excited whenever he pops up on tv. He was even on the Colbert Report 
Also, Family Guy seemed to believe that Stephen Hawkings teaches at my university, which is unfortunately not the case.
I took a class in the ethics/biology/other aspects of human-animal interrelationships from Prof. Patricia McConnell, who is the co-host of a NPR-syndicated radio show “Calling All Pets” and author of a number of dog behavior/training books.
For one class, she took us to the nearby livestock “show” building (the campus had an Ag section) and brought along two of her Aussie sheepdogs - she raises sheep as well, you see - one well-trained and one just starting. She used their behavior to show proper herding behavior and how it develops out of more wolf-like stalking behavior.
I took an evidence class from the guy who convicted Ernesto Miranda in his retrial. He also resigned as D.A. in Phoenix after the Don Bolles murder, a Mafia hit in the 1970’s. You never heard of him.
The man I would like to take a class from is Tom Lehrer who I heard teaches still at UC Santa Cruz (Math and musical theater), although neither of his subjects interest me he is so funny I would pay attention anyway.
I took a course in Heat Transfer from John Tichy, who was one of the founding members of Commander Cody and his Lost Planet Airmen. Once we found out he had toured with the Grateful Dead, it explained a lot.
Not really a ‘professor’. But in fifth or sixth grade my class spent a few days being taught about writing and poetry by Shel Silverstein. He went to school with my teacher and guested every couple of years.
Having him read his own stuff was great.
The closest I ever got was one of my political science professors who hosted a “Meet The Press” type show on our local television station.
I could have taken classes from (then-future, now-late) Senator Paul Wellstone when I was in college, but Political Science wasn’t my thing.
My first semester in grad school, I TA’ed for Wolfgang Haken, who’s a celebrity in mathematical circles for co-proving the Four Color Theorem.
I’ve had several professors who were published novelists/composers/textbook writers/et al, but probably none famous enough to count as a celebrity.
My undergraduate adviser was Walter Alvarez, who (along with his Nobel-laureate father, Luis, and Frank Asaro) proposed the hypothesis (now supported by significant evidence) that the mass extinctions at the end of the Cretaceous were caused by the impact of a large (~10 km diameter) asteroid or comet.
In graduate school I sat in on (but did not enroll in) one of Tom Lehrer’s math classes. Great lecturer, he made the material more interesting than the fact that it was presented by a former celebrity known for his stage presence…
These two aren’t national celebrities, but I had classes with two women, one of whom is a drive-time DJ, and the other, who had been a morning TV news anchor/reporter who left to teach. Both of them swear by Mountain Dew. 
Robin
Depends on what constitutes “celebrity”.
I had a musicology professor as both an undergrad and grad student who’s one of the leading authorities on Berlioz. My voice teacher (and vocal pedagogy and vocal lit professor) was fairly well known in the opera world in his day (sang relatively extensively with people like Sherrill Milnes and Beverly Sills). My orchestration professor is a composer who is at least somewhat well known in Eastern Europe (the Slovakian Radio Orchestra seems to like her stuff). My choral arranging and choral methods professor was in a world champion barbershop quartet and directs a recent world champion barbershop choir.
Miller’s fantastic! I found his lecture The Collapse of Intelligent Design linked from The Church of the Flying Spaghetti Monster. I intended to only watch a little but ended up watching the entire lecture through twice. Then of course I had to go read his book .
That’s so cool that you’ve had a class with him. 
I took an art class from Wayne Thiebaud at UC Davis. He is one of my favorite artists. Almost everyone on the faculty at the time was a world famous artist.
I didn’t take his class, but I knew (Pulitzer Prize winning journalist and memoirist) Rick Bragg when we were both on faculty at U of AL. Those I knew who did take his class described him as a great guy but terribly disorganized lecturer, and he himself admitted that he’d never had respect for college professors until becoming one and realizing “It really is work!” (Bragg grew up very famously very-blue collar and regarded profs [by his own admission] as ivory tower eggheads who pontifficated for an hour a few times per week then went home.)
It’s very common to see John Lithgow and Michael Dukakis on the UCLA campus.
I guess the closest I got was attending a lecture in Norway by Jose Ramos Horta. I dunno if he counts as a celebrity per se. He was a brilliant speaker, at any rate.
I took piano lessons with Charles Siegel, who was once a huge jazz pianist in South Africa, releasing dozens of albums.
Before he acquired a modicum of fame in avant-jazz circles, I took twelve-tone and microtone composition with Joe Maneri.
My brother was recently made an honorary professor of computer science, does that count?
Some lower level archaeology survey type class from Brian Fagan. No contact with him directly – I was one of 500 or so students in the lecture hall.
Good class, though.
I once told my college advisor that a physics prof of mine had informed the class that if certain members of the class couldn’t make it through his class that they should go ahead and switch majors. My advisor (a physics prof himself) said that he’d been told the same thing by Luis Alvarez.
I took an awesome class during graduate school at Harvard that was taught by Stephen Jay Gould and Alan Dershowitz (and also by Harvey Cox, a theologian at Harvard who isn’t afaik famous). The class was called Thinking About Thinking and it really was one of the best classes I’ve ever taken (oh, and Natalie Portman was a fellow student…). Here’s a link describing the class:
http://www.hno.harvard.edu/gazette/2000/04.13/think.html
-Tofer
p.s. Sadly, Stephen Jay Gould died a few days after our final. He had been sick most of the term but he still presented at most of the lectures.