The iOS 5 update to use Find My iPhone is good. If you've had an iPhone 4 (4S) then you could've been on that a while ago but now iOS5 supports 3GS.
BUT if you're looking at something that's pin-point accurate and you're allowed to literally 'watch' your phone and see it on a map over a course of a few hours, then I would suggest jailbreaking your iPhone and getting
iLocalis.
No, it's not free. You have the $5/year option and a $20/year option. I would highly suggest the $20 option since it allows you to do a LOT more things with it and in my opinion, it definitely is worth it.
The best features in the premium is the fact you'll have better Push support (so you can receive commands faster and you'll be able to ask your iPhone for it's location at any time), and you'll be able to lock the uninstallation of iLocalis so it's not possible to remove it.
It works in Safe Mode as well, since it has a dylib at the root level. The site doesn't go down, it's not slow, and it's still in constant support right now.