What's the protocol for post-interview thank you notes?

Can I send an e-mail or do I send a handwritten note? What do I say in here exactly? Obviously the standard "thanks for the opportunity to meet with you" but is stuff like "I look forward to hearing from you (or working with you)" too suggestive? I really clicked with this interviewer and she expressed sincere interest in me and my qualifications so now she is going to p me along to the next step in the hiring process under her boss.