The Collaborative International Dictionary of English v.0.48:

Subscriber \Sub*scrib"er\, n.
   1. One who subscribes; one who contributes to an undertaking
      by subscribing.
      [1913 Webster]

   2. One who enters his name for a paper, book, map, or the
      like. --Dryden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

subscriber
    n 1: someone who expresses strong approval [syn: subscriber,
         endorser, indorser, ratifier]
    2: someone who contracts to receive and pay for a service or a
       certain number of issues of a publication [syn: subscriber,
       reader]
    3: someone who contributes (or promises to contribute) a sum of
       money [syn: subscriber, contributor]

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "subscriber":
   Maecenas, Santa Claus, almoner, almsgiver, angel, approver,
   assignor, awarder, backer, bestower, certifier, cheerful giver,
   conferrer, confirmer, consignor, contributor, cosignatory,
   cosigner, donator, donor, endorser, fairy godmother, feoffor,
   financer, funder, giver, grantor, guarantor, imparter, insurer,
   lady bountiful, notary, notary public, party, patron, patroness,
   philanthropist, presenter, ratifier, settler, signatory,
   sugar daddy, supporter, testate, testator, testatrix, underwriter,
   upholder, vouchsafer