What makes a good slogan?

As we've been studying about Public Relations and Advertising we've been considering what makes a good slogan or tag line for a company. The first ones that come to our minds are very different and we're not sure what the common thread is that makes them memorable. Anyway, here are some of our favorites from the past couple years:

1. Pepsi: For those who think young!


2. 15 minutes or less could save you 15% or more on your car insurance


3. There's a map for that (Woohoo verizon!!)


4. Are you in good hands? That's allstates stand

Those are some of the ones that are on our mind right now? What are some of your favorites? And why? Additionally, if we had a product right now to promote we'd want to use this slogan:

" It's like the first time, everytime"

Booyakashaaa. Feel free to borrow that. No credit needed.

ps. The picture above is of a Sabre Award "Superior Achievement in Branding and Reputation", awarded by the Holmes Report to PR firms that show innovation in their strategic planning. OH REALLY??? ha we know right, but just thought you should know.