The call for papers for the 40th International Workshop on Graph-Theoretic Concepts in Computer Science is now online; submissions are due March 1. The actual conference will be in late June, at a chateau near Orléans, France.
For those who don't know, WG is centered on the topic of graph algorithms, and (more than many other algorithms conferences) welcomes research involving special classes of graphs. Despite the name I think it's more of a symposium than a workshop: that is, it consists of presentations of selected papers, which are collected in a proceedings, rather than having working groups, more informal talks about in-progress research, and no proceedings. It's somewhat but not highly selective: for instance, in 2009, the acceptance rate was around 40%. It's held annually, usually in central Europe. I'd go a lot more often if it weren't so far away from me.