Online resources for summer schools in software engineering?
I would say that one of the best online resources for Software Engineering is SEWORLD. You can browse their archives and look for summer schools there. 

Note that their search engine is a bit weird, if you go through "search the archive", put Summer school in the subject and "2010-1-1" in the starting date (when I leave it blank, I don't get recent results). For future references, here is the result of this query: 


ISSSE 2012 - 9th International Summer School on Software Engineering
Summer School Marktoberdorf 2012] Call for Application
LASER Summer School 2012: Innovative Languages for Software Engineering
CALL FOR PARTICIPATION - 4th RiSE International Summer School (RISS) - Next Generation of Software Product Lines
summer school VTSA 2011
Summer School on Technologies for Realizing Social Networks and Applications
CFP: 1st Insubria International Summer School on Open Source Software (IISSOSS 2011)
Summer School on Mechanized Logic for High Assurance Software
Canadian Summer School on Practical Analyses of Software Engineering Data
UPCRC Illinois Offers Summer School on Multicore Programming
3rd International CASE Summer School on Practical Experimentation in Software Engineering - July 11-15, 2011 - Free University of Bolzano-Bozen
Summer School on Programming Languages for Concurrent and Parallel Computing
8th International Summer School on Software Engineering (ISSSE 2011)
[Summer School Marktoberdorf 2011] Call for Application
LASER Summer School 2011: Tools for Practical Software Verification
[CFA] Summer School on Programming Languages PL2010
CALL FOR PARTICIPATION - 3rd RiSE International Summer School (RiSS) - Generative Reuse
Call for participation to the 3rd International Summer School on Adaptive Socio-Technical Pervasive Systems
CfP ADAPT Summer School
DSM-TP 2010: 1st International Summer School on Domain Specific Modeling - Theory and Practice - Call for participation
Call for participation: VTSA 2010 Summer School on Verification Technology, Systems &amp; Applications
6th REASONING WEB Summer School "Semantic Technologies for Software Engineering"
Summer School on Mining Software Repositories - June 2010, Kingston, Canada
CfP: UPCRC Illinois Summer School on Multicore Programming
LASER Summer School on Software Engineering
TiC'10: Third International Summer School on Trends in Concurrency
Call for Part: CASE Summer School, Bolzano, Italy, 19-23 July 2010
CfPart: 6th TAROT Summer School on Software Testing
7th International Summer School on Software Engineering