There are tons of free websites that provide ideas for teachers performing basic chemistry experiments (a few listed below). Also this book
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seems to be advertised a lot on these websites if you want a printed resource. Don't shy away from the experiments geared for students in elementary school, the concepts are applicable to any age group. You can just present a more in depth discussion on the materials for your high-schoolers.

You'll see a lot of repeat experiments in the following websites. These will most likely be the easiest to perform and/or the most impacting, especially if everyone is toting them as a good classroom experiments. While you are investigating the experiments, check to see them on www.youtube.com. There's a good chance that any experiment that's worthwhile will have already been video taped and demonstrated there. You may also get pointers or additional info from the teacher presenting it in the video.

List and list of ideas at:
USA's National Science Foundation recommended sites
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Good homework/final project assignments
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Specific ideas I've personally seen in high school:
Famous Mentos experiment
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See the youtube.com links at the end
o Messy, do outside!
Non-Newtonian fluid
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See the youtube.com links at the end
Easy, interactive, a bit messy
Colored flame test
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o Easy, requires a Bunsen burner, and relevant materials

It is great to see a teacher committed to doing demonstrations for their students. Such demos were the exact things that got me interested in chemistry and science!