This will be different and fun. Planet Catfish has lots of cory info. Are the blue ones those that you're interested in? The Habrosus are really small so I'd skip those in a 75. I have Melinis in my 20 long and think they're great - love the stripes, and they're more of a chunky bodied cory. They look really cool swimming around together even my small group of 5. A bigger group would be sweet. I have them on black sand, though, and their bodies darken on it so they are not as striking in contrast on black. I'd go with a bit lighter substrate if you chose them.
Have you narrowed down the other tankmates yet?
I would steer you away from the CPDs, because they are really tiny and kind of shy. They're so small that it's hard to see how beautiful they are, and they might get lost in a 75. I just got some glowlight Danios (Danio Choprae) for my 20L and they are really active, hang out together, and are a nice flash of color. A huge group of those could look really cool. Wet Spot has those, too.
