NIST Internet Time Service
Here is an app that I've used for years on my desktops, that lends itself quite well to portability on USB drives.
It's the actual NIST Internet Time Service or NIST as commonly referred to. It's a single self executing file (exe), and I'm using it right now on my USB drive to accurately set the time on a PCs internal clock via any internet connection.
It's a handy little tool for use as part of any general tune-up on a friend or customer's PC.
The app can be downloaded from NIST Internet Time Service, at:
http://tf.nist.gov/service/its.htm
- Paul A), and I'm wondering what the general feeling is about them for being portable apps, as you would have to have the .net framework installed first before it can be used... but the same goes for JRE.