The University has a lovely little natural history museum, and they have a lovely educational department that loans out "museum in a box" kits to teachers. The kits come full of specimens and books and so forth, and a 3-ring binder of lesson plans. With the budget cuts that are hitting almost everyone, they've raised the rental fees on these boxes, but it still seems worth it to me.
We've had a box of Rocks and Minerals for two weeks, and we've been working through the lesson plans. It has been a fun unit study, all packed and ready to go for me!
I don't know how many people even know about this resource. If you have a museum or a University near you, you should check what sort of teacher resources they have. These resources are available for homeschoolers too!