OptimalIdM has announce support for Microsoft WIF (you can get more info here). What they have done is pretty interesting. The have created an STS that front ends their Virtual Directory. This allows a single STS to be used to issue claims against multiple identity stores.
Of course the main use case here is the multiple AD forest scenario, but it could also support disparate identity stores such as other LDAP directories, databases, etc.
[Full disclosure: I have done consulting work for OptimalIdm in the past.]