another voice for email.
this is more or less my template for those:
Dear ____,
Thank you for the opportunity on Monday to interview for the available ___ position at [x]. I appreciate your consideration and enjoyed speaking to you, [other interviewers]. After our conversation, I am that much more confident in my ability to perform well in your group. My experience and familiarity with [necessary skills/abilities] provides a solid foundation for this role, and my interest in growing my understanding of [new work or task] suits me for the work involved.
I especially appreciate that [x] is [something the company is doing that ties to your personal goals/interests). Being able to affect [this process] by providing meaningful analyses is what I find most interesting about [this kind of] work, and it is exciting to know I would be part of a group that does just that. I like that you specifically mentioned [something they specifically mentioned about the work that you also enjoy - this follows up to a question I ask in the interview, "what do you most enjoy about working for XXX").
Thank you again for your consideration, and I and look forward to hearing from you all soon regarding this position. Please feel free to contact me at any time if further information is needed, either by phone or by email.
Sincerely,
...some might argue this is too lengthy; I disagree and think it's important to sound as personable and well-suited for the job as possible, using whatever information you learned in the interview that makes you feel like you're the best for the job.