One of the charity's I am working with is planning to carry out a deep evaluation of its programmes, including a longitudinal study to look beyond its outcomes towards full on impact.  I am very excited. We have a couple of potential partners in mind but want to cast our net wider as we're sure there is great practice out there.  Who have you used for your evaluations who you would rate as truly excellent?  Where should I advertise this to attract (high quality) proposals from potential partners?

And, on this occasion, this is an invitation for people on his forum to suggest themselves and promote their credentials.  

An request for proposals should be out by end March.