I like catalina, there are a couple of fish you run into in the trade, catalina gobies are common, and scyth butterflies are common there, but below 80 ft so you wouldn't see them while snorkeling.
Still. the water there is cold, so if you don't want HI because of your senior trip try the east coast of FL, I could point you to some places where you could collect your own tropicals while snorkeling. You just need a one week fishing license (or weekend license depending on your stay) and you can bring everything you collect back. You can't take any stoney corals but there are plenty of very attractive soft corals and zoo's you could bring back.
Things you would find would be 4 species of angel, maybe a 5th (sometimes you wont find rock beauties in shallow, but queen, blue, french and grey are common in shallow) lots of wrasses and 4 species of butterfly, (though 3 are only so so as aquarium fish because of diet) condylactus anemones, plus 3 or 4 lesser known but good aquarium animones, feather dusters coral banded shrimp, and anemone shrimp- I could go on and on but you get the picture. Ask Paul Betito (pbetito) and Aaron (Airinhere), they both came out to visit me on a couple of different occasions and brought their catch back. They scuba, but I know lots of snorkeling spots I could direct you to if you choose.