The main conference papers are published by Springer:

ECOOP - Object-Oriented Programming
21th European Conference, Berlin, Germany, July 30 - August 3, 2007, Proceedings
Series: Lecture Notes in Computer Science , Vol. 4609
Sublibrary: Programming and Software Engineering
Ernst, Erik (Ed.)
2007, XIII, 625 p., Softcover
ISBN: 978-3-540-73588-5
Online version available

The workshop papers are available via the workshop pages. Some workshop proceedings are published as technical reports by the TU Berlin, Faculty of Electrical Engineering and Computer Science, and are available via http://iv.tu-berlin.de/TechnBerichte/tb2007.html.

A workshop reader is to be published in the Springer LNCS series.