Russia: Moscow Conservatory

This definitive stamp (Scott 6433) features the organ at the Moscow Conservatory in Russia. This stamp was issued in 1998, following currency re-valuation. A similar stamp was issued two years before, with high-denominations, before the currency change. Another stamp was issued in 1999 with the same design and denomination, but with a change in the vertical lines of the shading. The organ and Piotr was built by the Cavaille-Coll firm of France. A relationship between organist-composer Charles-Marie Widor and Piotr Illyich Tchaikovsky led to the decision to work with Cavaille-Coll. Apparently Widor felt a French builder could best capture the pathos of Russian musical sensitivities in the new organ. The new instrument was built in 1896, but went first to the Paris Exhibition before being installed in the conservatory, an interestingly circuitous route. After work on the instrument three times in the imd- to late 1900's, by the 1990's heating and cooling issued in the hall had damaged the organ such that it was unplayable.

Note: there are 3 versions of this stamp:
1997, 5000 rubles, Scott 6382
1998, 5 rubles, Scott 6433
1999, 5 rubles, redrawn, with micro-printing replacing the vertical lines in the background, Scott 6560
I have the 1998 pictured here, and it's the only version I own.

Belgium: Ninove, Bastogne

These are the third and four in a set of four stamps issued by Belgium in 2000 for tourism. Scott #1824 depicts the exterior of the Church of the Ascension in Ninove and its organ. The last (Scott #1825) depicts the parish church at Bastogne and the organ there. One can find just a bit more inforamtion about each of these four stamps and the church depicted here.

Belgium: Grimbergen, Mons

These two stamps are a set of four issued by Belgium in 2000 for promotion of tourism. All four stamps depict a rendering of the exterior of the church building, plus a view of the organ. The first (Scott 1822) stamp features the organ at the Norbertine Abbey in Grimbergen. The second (Scott #1823) is that of La Collegiale Sainte-Waudru. Here is a nice article on the builder, Delmotte.

Belgium: Flor Peeters

This stamp (Scott #1631) was issued in 1996 as part of a set of four stamps honoring musicians and writers. Flor Peeters (1903-1986) was a church musician and prolific composer of music, including many works for organ. The organ in the stamp is that of the church most closely associated with Peeters, that in Mechelen. Also shown here is a photo of the interior of the church looking down the nave toward the west (rear) gallery.

Austria: Catholic Church Music Congress

This stamp (Scott 596) depicts the organ at the St. Florian abbey, of Anton Bruckner fame. The stamp was issued in conjunction with the Second International Congress for Catholic Church Music, held in Vienna in 1954.

Austria: Albrechtsberger

This stamp was issued Janury 31, 1986 to commemorate the 250th anniversary of the birth of Johann Georg Albrechtsberger. Albrechtsberger was born in Klosterneuburg, near Vienna in 1736. As church musician he worked in Raab and Maria Taferl. He ultimately was kapellmeister at the St. Stephen's Dom in Vienna. It is hard to determine which organ is depicted in the background of the stamp. The stamp depicts only part of the facade of an instrument. However it looks very much like the complete facade shown below. It seems to be the instrument in Klosterneuberg, built by Freundt in 1642.  The abbey is an Augustinian house on the Danube river.

Notes from 2012: This site has a nice history of the facility and the organ. (The developer of the site sadly died in February 2012; his site is wonderfully detailed, with many videos of the organs he covers.) Here is a specification since 1990 after work by Kuhn of Manndorf, Switzerland:

Ruckpositiv (I)

Nachthorn        8
Prinzipal          4
Klein Copl       4
Spitzfloeten     4
Octave             2
Superoctav       1 (3)
Cimbal scharf  ¼ (3)
Krummhorn     8 (2)

Hauptwerk (II)

Principal          8
Principalfloten 8 (6)
Copl                 8
Quintadena      8
Octav               4
Octav Copl      4
Dulcian            4 (3)
Offne Floeten  4
Quint               3
Superoctav      2
Mixtur             4, XII-XIV (3, 6)
Cimbel gross   2/3 (3)
Dulcian          16 (1, 6)
Pusaun             8 (1, 6)

Brustwerk (III)

Coplfloeten      4
Prinzipal          2
Spitzfloeten     2
Regal               8
Tremulant (4)

Pedal

Prinzipal          16 (5)
Subbass           16 (6)
Octav               8
Choralfloeten   8
Superoctav       4
Mixtur              4, VII-VIII
Rauschwerk     2, III
Grosspusaun    16 (1, 6)
Octav Pusaun   8 (1, 6)
 
1990 Installation: 1
1984 Installation: 2
1950 Installation: 3
1934 Installation: 4
With an extra key B below low C: 5
Activated/Deactivated ventil stop “Wind Hinterladen”: 6

Austria: Music Academy

Austria issued this stamp (Scott 864) on June 5, 1970. It depicts the organ in the Great Hall at the Vienna Music Academy. 1970 was the centenary of the building's construction. This site gives several pictures of the organ, but does not give a stoplist, nor the name of the builder.

Update as of 4/2011: Reiger has built a new organ within the pre-existing case. They have a specification here. This discussion board reveals that the original organ was by Ladegast, completed in 1872. The new instrument has 84 ranks at a cost of $1.8 Euros. If the board information is correct, the inaugural concert should have been held recently. The work has been going on since 2010.