When I'm feeling a 'bikers high' it's usually:

"Allez! Allez! Allez!"

I've even said it out loud!

When I'm struggling it's a fairly simple:

"Do it!" Over and over again in my head.

Yeah, not real interesting, but it does the trick! My favorite is the joyful "Allez!" exclamations though. Just reminds me how much I love being on my bike.