However, I decided that they would stick very closely to the Codex as far as heraldry. Here's what I've got so far, and I'd appreciate comments:
assault marine, Second Company
devastator sergeant w/ Mk VIII armor, Third Company
captain, Fourth Company
For regular power-armored marines, I went with the company color being displayed on the squad badge on the right pauldron as well as on the squad number on the left knee.
termie with power fist, First Company
For the termies, helmet is company color as is the squad badge on the right knee. This is the one on which I went back and forth the most. I was toying with the idea of doing the power fist in a bright, caution-tape yellow or something similar, or in the orange of the pauldron trim. Also wasn't sure if I should do the armor behind the helmet in one of the grays. Thoughts?
apothecary
I used a slightly off-color power fist to represent the narthecium.

techmarine
Going with the black theme, I gave the techmarine a darker, rusty red rather than the brighter red more commonly seen on techmarines. Unfortunately, I didn't have a servo-harness or power axe to include in the pic.
lexicanium of the Librarium
Again. I didn't have a psychic hood, so I decided to use the pic to indicate a lexicanium.