I'm a software developer at Analytical Graphics Inc., where I contribute to the STK Components product. I'm also a GPS subject matter expert, specializing in the fields of GPS satellite accuracy and receiver accuracy.
I also write web services and I'm the principal developer for AGI's Analytical Services.
The analytical services documentation is located here. If you'd like to try them out, contact me - I can get you a demo API key. Also, there are videos describing how to use them at the bottom of the main page.
This application lets you use a few of the GPS services I've made available.
This application will show you the position of any satellite as well as the countries it flies over. You can also see which of four satellites will pass over you within the next week.