I have been a "friend" of the Henley Forum for Organisational Learning and Knowledge Strategies (known as the Henley Forum) since its inception in 2000..
It has done some great work over those years - some of it published freely online. Take a look at their Knowledge in Action series of leaflets for example (over 30 of them) such as this one
on Evaluating communities of practice: adopting learning-oriented approaches - really good, useful material if you are working in KM or even if you are not!
They also run an annual conference and regular workshops.
Most of these events are only open to members but increasingly they are making a small number of places available to non-members.
They have a 2-day Advanced Course in Knowledge Management facilitated by Dr Christine van Winkelen coming up in July. for example. I often get people asking me where they can find a really good Knowledge Management course and this is one - go take a look.