the fresher and more local your veggies, the better they will taste even with no seasoning. I don't usually season simple steamed veggies, but on occasion I squeeze fresh lemon on, or use a lot of pepper, and of course, fresh garlic is always good.
Agnes is right about roasting making them taste better too. I LOVE green beans roasted with a little bit of garlic and red onion, that's probably my favorite. YUM.