What do I need to do to securely "wipe-out" my iPhone before selling it?

[macaddict23]

Sorry if this is a repost.

I made up my mind, and I'm finally going to list this on eBay. Before I ship it out to the buyer, what do I need to do to clean out my personal information?

Is it just a matter of plugging it into iTunes and clicking the Restore button?

Do I keep the SIM card?

Thanks in advance!