Well, I`m not a marketing or a branding specialist, just a regular little person and Nike already said "Just Do It" so we can`t use that, but, maybe we could go one better and say:
"I Did It" with StartupNation
Or does that sound porno?
It`s your future ~ StartItUp!
Other : mugs, t-shirts, briefs, caps, cereal, etc. w/ SuN logo
"Smartest UpStart in the Nation!" - mug
sportzbriefs - "StartMeUp!"
"Start Up Native" - mug, t-shirt with avatar
"Start Up Nation Spirit!" - mug, cap
"Start It Up ~ Keep It Going!" - t-shirt
"Start Up Your Smarts" - vitamins
For Mompreneurs - "Let`s Start This Baby Up!"
4th of July - *StartUpNation Celebration!*
"Start It Up in Style!" - adverstising
aprons - "StartItUp Saucy and Bring To A Boil!"
Or - "Now that`s a spicy startup!"
StartUpperware - tupperware
Start Up Nation Cereal - "We know it`s tough - Keep chewing"
I hope that`s enough, for now.

I just LOVE Nikole`s baby onesie idea. I would capitalize "ME" or underline it to emphasize that part.
Oh, also just so you know, Mompreneur is a trademarked name. Ellen and Pat own it over at mompreneursonline.com.