I've really enjoyed the Behind the Seeds tour, and have taken the tour maybe 4 times, over the past 6-7 years. It's very reasonably priced (also, if you happen to buy the Birnbaum's Guide to WDW, there is a coupon in the back.)
The other thing I like about it, is that it doesn't take a half day or longer, like some other tours. It's just an hour, and it's really interesting and informative. I'm a fan of (behind-the-scenes) activities, and this tour does not disappoint. They often have (horticultural) university student CMs from Florida who lead the tours, and they are helpful and knowledgeable. Tour size is about 12-15 people, so there's ample opportunities for people to ask questions.