You may find the following useful:

Music Room   On line shop for sheet music, discounts for large orders.

Chorus Rehearsal One of many useful sites for choir rehearsal parts in down-loadable format. Some public domain (free) and some on CD (Very cheap)

Choraline - Sheet music, rehearsal CDs and tapes and also the site where I got our choir folders. Gives a 10% discount to Choir Members (Used to be 'Music Dynamics')

Cyber Bass   A listing site I use for hunting MP3 and midi files for rehearsals. Links to loads including the splendid Silvis Woodshed

British Choirs on the Net   self explanatory really.

Making Music  -  represent and support over 2,800 voluntary and amateur music groups throughout the UK, including choirs, orchestras, music promoters, samba bands, jazz groups, festivals, handbell ringers, barbershop choruses, brass bands, and more...