The whole gang's in here, from Urdnot Wrex (The Quad-Kicker: rum, bourbon, ginger ale, and curry) to James Vega (The Rojo Loco: dark rum, raspberry, cranberry, and lime).
They're all fun and clever, but for descriptions, my favorite is Garrus's drink, "The Heat Sink":
With equal parts Jagermeister, Blue Curacao and Mountain Dew, The Heat Sink is strong and effective, but it tastes awful. So ingest at your own risk.
I don't think I could drink it, though. For actual consuming, I think I'd go with Tali's "Keelah Se'lemonade," featuring Parfait d'Amour, Mandarin Liqueur, vodka, and lemonade. Though I'd also love to see an Illusive Man drink, even if it would no doubt turn a muddy purple as soon as you touched the glass.
As for the Commander? Well, you'll have to come up with your own drink for Shepard, just as you have to come up with your own Commander. Personally, I think mine's a bourbon drinker who secretly enjoys a frozen strawberry daiquiri on occasion.
Just drink responsibly: you don't want to end up pulling an Ashley. You'll regret it when your commander spends the rest of the game making fun of you.