Updates
November 1, 2012: a reader (thank you) has provided an even better map/data base -- worldwide CNG locations and PRICES. Prices are 75 cents in Alberta, Canada, vs $2.00 in Austin, Texas.
Original Post
This is an interesting map: CNG - LNG filling station locators. The legend at the left at the link allows one to click on/off current stations and stations that are planned.
It is interesting to see the Flying J corridor across I-80 from California to Chicago. Similarly, I-10 from southern California to Dallas, Texas, and then all the way to Jacksonville, Florida.
The Denver area is also particularly interesting.