Network Security Services libraries
NSS implements SSL v2 and v3, TLS, PKCS#5, PKCS#7, PKCS#11, PKCS#12, S/MIME, X.509v3 certificates, and other security standards. These libraries are used by Mozilla / Netscape Communicator and server products. [Open Source]

Claymore PureTLS
Java SSL Implementation. Supports SSLv2, SSLv3, TLSv1. Uses Crypto library from Cryptix. [Open Source]

SSL Library
Java Library. Implements SSLv3 and backward compatible SSLv2. [Open Source]

GNU TLS
An Open Source implementation of TLS 1.0 Internet protocol as described in RFC2246. [GPL]

SecureBlackbox
Delphi/Kylix component and ActiveX/DLL library [Commercial]

Open SSL
Collaborative effort to develop a full-featured, and Open Source toolkit implementing the secure sockets layer (SSL v2/v3) and transport layer security (TLS v1) protocols.

Java Secure Socket Extension
Sun's official extension for SSL communication in Java. API allows third party library being used as a provider.