St Alban's Abbey, Hertfordshire, Great Britain

This card shows "The Nave, St. Albans Cathedral" with the organ in the distance. The building is built on the site where St Alban died for his faith. The cathedral website gives information about the current instrument, built in 1962 by Harrison and Harrison, but I could not readily find information here about the previous instrument(s). I'll keep exploring. I found the card below on a genealogy site for Herfordshire, with several old postcards of the interior and exterior of the abbey/cathedral. The present church was begun in 1077, replacing an even earlier Benedictine monastery. Following dissolution by King Henry VII, the facility fell into decline, such that by 1832 part of the south wall collapsed. Repair work began, and in 1877 the abbey became the cathedral for the new Hertfordshire area.

Update: 16 December 2013:
I was able to get a little bit of information from the National Pipe Organ Register of the British Institute of Organ Studies about the organ. Given the general time parameters of the post card's image, I list below a time frame of organ activity at the cathedral that would seem to be most relevant.

1881: The Hill firm rebuilt the existing organ and moved it to the rood screen, which is where it seems to be in both of these card images.
1885: Abbott and Smith undertook an enlargement of the instrument and did some remodeling, including providing a new west-facing pipe front
1906/8: Abbott and Smith rebuilt and enlarged the instrument
1921: Tunks and Sons made some tonal changes on the organ

Virginia, USA, Pohick Episcopal

This more modern card conveniently includes plenty of useful information about the organ pictured. It is located in the Pohick Episcopal Church in Fairfax County, Virginia. The instrument (click on "Pipe Organ") was built by the Noack firm in 1968 and includes 13 stops, 17 ranks, totaling 880 pipes.

Virginia, USA, Methodist Episcopal Church

This card simply says "Interior Epworth M.E. Church, Va." on the picture side.  The color card is used. The postmark reads "Washington, DC Aug 6, 1909, 3PM." I've tried looking for historical Methodist churches in the Northern Virginia region without much luck. The Methodist Episcopal denomination eventually became part of what is now the United Methodist Church. However, "Epworth" is a pretty common name for Methodist churches, given its association with John Wesley. It may be possible to find historical information about ME church in that region, but that will have to wait for another time. Absent information about the church, it's difficult to know much about the instrument. If you know anything about this church, please let me know in the comments.

Passau, Domorgel

The organ in the Passau Cathedral has long been famous for being one of the largest in the world. I believe it is currently still the largest church instrument in Europe. This card features the console.The five manuals are only slightly less intimidating than the setter buttons for the combination action. The post card is not that old; if I read the postmark correctly, it's from 1958. The organ currently has 5 manuals, and 233 ranks, and nearly 18,000 pipes.