Preludes in all the keys

[dax]

Christopher Hobbs (b.1950) - 24 Preludes in all the keys (1992).

[Okon Fuoko]

Hello to all of You!
In the category of 24 Preludes there are also the early Ferrucio Busoni and the more obscure (and more fine!) Finnish Erkki Melartin's examples, as well as Miecszyslaw Vajnberg's set for the solo cello. 
Speaking about 24 Preludes & Fugas I must mention two sets from the Soviet composers in the footprint of Shostakovich: Rodion Shchedrin (Great set!) and Sergei Slonimsky.
And - as the last but not least - Niels Viggo Bentzon's Tempered Piano: 13 sets of 24 Preludes & Fugas (covering the total of 15 cd:s)!!

[isokani]

Semyon Barmotin.
Felix Blumenfeld.
Busoni (v early, not sure there are 24 though).
Bacarisse.
Barvynsky.
Kasyanov
Mushel (pr. + fugues).
Shirinsky.
Golts.
Casadesus.
Kabalevsky.
Karaev.
Heller.
Kapustin.
Palmgren.
Abramian.
Gal.

[saxtromba]

So far as I know, there's only one composer who actually wrote music in all the major and minor keys: Johann Christian Heinrich Rinck (1770-1846), who wrote two sets, each of 30 pieces, covering even the rarely used enharmonic keys (a# minor, C# Major, Ab minor, and Cb Major).  One set, Op. 55 for organ, was Preludes; the other, for piano, Op. 67, was 'Exercises'.

A brief bio, though one which doesn't mention his unique achievement: http://www.naxos.com/person/Johann_Heinrich_Christian_Rinck/26299.htm

[Rainolf]

The Silesian composer Gerhard Strecke (1890-1968) wrote 24 Preludes and Fugues for organ late in his life as his op. 101. I don't know this pieces, but they are sold by the Laumann Verlag in Dülmen, which is specialized on Silesian music.

[kb]

From Norway, I know these collections for piano solo:
Trygve Madsen: 24 preludes Op. 20 / 24 preludes and fugues Op. 101
Frank Tveor Nordensten: 24 preludes and fugues
Filip Sande: 24 interludes / 24 preludes and fugues

[doctorpresume]

A vote here for Goldenweiser's "Contrapuntal Sketches", opus 12, a cycle of 24 pieces (structured Prelude, Fugue, Canon, Prelude, Fugue, Canon etc) in all the keys. Marvellous recording by Jonathan Powell on the Toccata Classics label.

[eschiss1]

Not quite the same, but Dancla's op.115 is a set of scales, etudes and melodies in all the major and minor keys, if the Boston edition published by Whipple in 1881 and scanned in by the Library of Congress is accurate (the original title, L'utile et l'agréable (24 Mélodies) doesn't seem to suggest this.)
Eric