I was looking for someone like http://www.startssl.com/ for a long time: a real, trusted Certificate Authority with very good root cert ubiquity (wich would include iOS) that would issue free server certificates.
AffirmTrust, which is supposed to go online any day now, promises to issue free server certs for three year period. If their root CA certificate is going to be as widely distributed as StartSSL's, then it may be even a better deal than StartSSL, especially given that StartSSL web site and provisioning process are a little corky.