What’s a good way to wipe a hard drive for resale

For starters, encrypting your Home folder using FileVault (in the Security Preferences pane) is always a good idea. You might notice a bit of a performance hit (some people say they do, others don't notice a difference), but the tradeoff of additional security can give you some extra peace of mind.

As far as an iPhone-esque "wipe memory after [x] failed login attempts" function, the OS doesn't have anything like that built in, so you'd need to search out a 3rd party solution. I don't have any recommendations offhand for that, but likely someone else here could point you in the right direction.

Use the drive as little as possible. Plug it into an enclosure or simply boot the machine in TDM mode and connect it to another machine.

Pull over only the files you need (to minimize the time you spend accessing the drive).

You may want to do something like, just your ~/Desktop, ~/Documents, ~/Pictures, ~/Library/Mail, and ~/Library/Mail Downloads.

Do either: a) the biggest folders last, again, so that if the drive suddenly dies on you, you got as much stuff off it as possible, or; b) the most important folders first, such as any pictures you don't have backed up.