Shameless plug for my thread on brewery tours, etc:
http://www.flyertalk.com/forum/dinin...ou-travel.html

I will concur with the Boeing 747 / 777 line tour. I really enjoyed that - and this is from someone who works in factories all over as the environment for my product. I did enjoy the Guinness and Jameson tours - but they weren't really factory tours. Guinness is a tourist-oriented museum, but they payoff at the end is fantastic :D Jameson isn't even made at the location where you take the tour anymore. Still, the guides are entertaining and there is whiskey at the end. I never really thought of wineries / breweries as factory tours, but of course they are making product so why not? I'd heartily recommend the Sprecher Brewery tour in Milwaukee. Also, while I personally was not overwhelmed with the Celestial Seasonings factory tour in Boulder, CO - there is no better place in the entire world than the "peppermint vault" if you need to clear out your sinuses. Wow is that effective!

Even though I've taken the tour, I'm still pretty sure Budweiser is clydesdale piss ;)

If that's the Jelly Belly factory close to Fairfield, Ca. Then there is a Budweiser factory close by .
:)

Ben & Jerry factory tour in VT!

Porsche Factory tour in either Stuttgart or Leipzig. Just beautiful watching those cars being made!

I'm not sure it qualifies as a factory tour, but the Aalsmeer Flower Auction (just outside of Amsterdam) is tremendous fun to visit. You walk on a skywalk over the enormous warehouse floor, where crates of flowers are zipping buy everywhere.

Waco Classic Aircraft Company in Battle Creek, MI. Pretty sure it has to be arranged ahead of time, and I think they only do it for groups. My model airplane club did the tour, and they take you around the shop floor showing how they make the planes. Was definitely pretty interesting since it's very similar to how our models go together. As I recall our guide said the normal tour runs about an hour, we were there about 3 hours.

This and this.

Oh, I forgot about the Louisville Slugger factory. For some reason I really enjoyed it.

Also if you're in eastern Washington state there is a string of wineries between Pasco and Walla Walla that will beat out anything in the Napa valley.

I went on the Rouge plant tour a few times nearly 50 years ago. It was unbelievably interesting then. On the other hand they also took us to a display center that Ford had which if I recall correctly showed the flying cars of the future, circa 2000, so who knows what it is like now. But it is definitely worth looking into the River Rouge plant tour to see what they currently do on the tour.

Another vote for the Boeing tour near Seattle. And I also liked the Sam Adams brewery tour in Boston.

I actually wasn't that impressed with the World of Coca-Cola in Atlanta. The don't bottle or make the stuff there, so it's not really a factory tour. The high point is definitively the international tasting room where you can try flavors they don't sell in the US.

Another vote for the Jelly Belly tour in Fairfield, CA. Very interesting for all ages and you get to taste a lot of jelly beans. The gift shop also has great bargains on their "Belly Flops".

Other recs:

Trumer Pils brewery tour in Berkeley, CA. There are usually only a few other people on the tour and the tour guide is one of the guys who does the brewing, so not just a tour guide that memorizes an FAQ. They take you pretty much everywhere in the brewery too. Much for interesting and enjoyable than tours I've done at Brooklyn Brewery, Pyramid and Red Hook. Mac and Jack's in Redmond, WA is another good brewery tour.

Theo Chocolate tour in Seattle, WA. Very interesting and you get to taste a lot of chocolate. If you're a foodie, you will enjoy and appreciate this one.

Trabant (DDR car) factory in Germany. I did it right after reunification and struggled with the German explanations, but it was fascinating.

The Bureau of Engraving and Printing in Fort Worth--this is where they print paper money. We happened to catch them during one of the two times per year they have guests from D.C. who talk about their specific jobs, including a guy who engraves plates and a woman who pieces together mutilated money people send in and reimburses them. She had great stories! Even without the guests, the tour was fascinating. Make sure you check their site before going--very restrictive about what they'll let you bring in.

Also enjoyed touring the Sandeman sherry production facilities in Jerez, Spain. Yes, there are samples.

Although I don't remember much about it now, I know I really enjoyed the tour of the Hershey factory when I was a kid.