Ask anyone what they remember about their biology class. Betcha' they say it was the dissections. I know, its not the most "politically correct" activity, but we don't study science to be politically correct. We study science to learn new things and have new experiences.
Frog dissection brings out something special in students that can be hard to reach. With tools in their hands they are free to explore and investigate in a way they may not do again, ever. It makes them curious, motivated, and happy! Of course, an alternative assignment is always available for students that have objections to dissecting an animal, but in 22 years of doing this activity, I've only had a handful of students that chose to do the alternative.
Hanging up helpful anatomical diagrams is a good way to encourage student independence. They match what they see to the diagram to identify the parts inside on their own. This really cuts down on their dependence on the teacher as a resource. Your role should be to guide the students! You can see they really are happy and involved!
Dissection promotes teamwork! I pair reluctant or squeamish students with an eager partner. Some students look forward to this activity all year!