If you are interested in international development - that is, in supporting a small organisation for international development volunteering in Berlin, or even in volunteering yourself - you might want to check out an organisation called Commit to Partnership. It's a grass-roots level approach, supporting small partner organisations abroad to realise projects they believe are of most importance to their community. For this, "Commit" sends teams of well-prepared volunteers to work with the partners for 5-8 weeks.
I'm still sporadically involved with them and have some experience with the British volunteering culture myself, and I think that this organisation might suit some of you. In fact, it all started as a spin-off of an organisation in Scotland called Edinburgh Global Partnerships (http://egp.eusa.ed.ac.uk/index.htm) four years ago, and the spirit and philosophy hasn't changed much.
The organisation is completely run by volunteers, mostly students. Obviously, native speakers can offer great support for this kind of work! Also, your experience with a very different culture of volunteering is very valuable (Germany itself needs some development aid in this field...).
There's all kinds of work to do (fundraising, publicity, "global learning" activities, partner contacts abroad and project development, various training for the teams, organisational stuff, ...), and you can contribute on a one-off or regular basis (it's not a full-time job, though). They have strong social network as well, so it's a good opportunity to meet like-minded people (and to improve your German, if you wish...).
They meet regularly at a bar called Hannibal at the Görlitzer Bahnhof (corner Skalitzer/Wiener Straße), first wednesday of each month (so the next date would be 7th of November). Unfortunately, their website (
www.com-mit.org) is only available in German at the moment, but you can email them (berlin@com-mit.org).
Jan