See also Homotopical algebraic geometry and refs there.
Stacks: Book draft on Fulton’s web page, probably more recent version on Kresch’s page: http://www.math.uzh.ch/index.php?pr_vo_det&key1=1287&key2=580&no_cache=1
For some lectures and references, see Anel
Brillian and brief intro in Toen Essen talk, to stacks, simplicial presheaves with various model structures, and the conceptual difference between simplicial sheaves and presheaves.
A web-based algebraic stacks project
There are some references at Wikipedia.
Very basic definitions can be found in a chapter of Basic bundle theory etc, in K-theory folder.
A french book that looks really good is Laumon and Moret-Bailly
Good introduction in first chapter of FGA
Hollander: Classifying algebraic stacks
Teleman and Simpson: De Rham\'s theorem for \\\\infty-stacks.
Notes by Giansiracusa on Orbifolds and stacks and algebraic spaces
One chapter in the notes of Mirkovic.
nlab algebraic stack
http://mathoverflow.net/questions/56962/what-about-stacks-of-categories-in-algebraic-geometry
http://ncatlab.org/nlab/show/derived+stack
http://www.ncatlab.org/nlab/show/infinity-stack
http://ncatlab.org/nlab/show/category+fibered+in+groupoids
Schapira introductory notes on sites, stacks etc. In Homol alg folder
Toen course, see folder cours under Toen web folder.
For the relation between higher stacks and the classical notion of stack, see Toen, file web unpubl msri2002.pdf.
Toen: Higher and derived stacks, a global overview. File web publ seatt.pdf. Also contains an intro to Segal cats, and some material on schematic homotopy types.
A summer school program:
Motivation: why stacks are needed. Basic example: moduli of curves of genus g. The 2-category of groupoids, schemes as functors, categories fibered in groupoids, pseudofunctors. The stack condition. Representable morphisms, definition of algebraic stack (in the sense of Deligne-Mumford). Quotient stacks, stacks associated to groupoids. The 2-category of stacks; open, closed substacks; topological space associated to a stack. Properties of stacks and of their morphisms; valuative criteria for separatedness and properness. Inertia stack. (Quasi)coherent sheaves on a stack, cohomology of sheaves. Main worked out examples: moduli of stable pointed curves, moduli of stable sheaves, weighted projective stacks and toric DM stacks. Infinitesimal study of moduli stacks and deformation theory. A short introduction to Artin stacks will also be provided.
Aim of Workshop. The Workshop is intended to discuss the state of the art in stacks and moduli theory. Up to now the following speakers have confirmed their participation: F. Catanese, G. Farkas, E. Sernesi, A. Verra, A. Vistoli.
http://mathematics.stackexchange.com/questions/727/algebraic-group-g-vs-algebraic-stack-bg
nLab page on Stack