Marianne Gullberg and John Williams (Cambridge) have just published a volume on second language acquisition that is part of The Encyclopedia of Applied Linguistics (Dec 2012).

The encyclopedia comprises over 1,100 original essays written by an international team of scholars from over 40 countries. It is a ground-breaking reference work, available online or as a 10-volume print set. It is a comprehensive resource covering 27 key areas of applied linguistics, ideal for students, teachers, researchers, and practitioners in the interdisciplinary field of applied linguistics.
The volume Cognitive second language acquisition, edited by Gullberg & Williams, contains 59 authoritative entries on everything from Brain activity during second language processing to Formulaic language and collocation, Learner varieties, and Task-based learning.
Gullberg, M. & Williams, J. (Eds.). (2012). Cognitive second language acquisition. (Volume 6 in the Enyclopedia of Applied Linguistics, Ed. C. Chapelle,  Online ISBN:9781405198431). Malden, MA: Wiley-Blackwell.