Nice review in Thomason: Symmetric monoidal categories model all connective spectra. (Thomason folder)
Brief note by Baez
http://www.ncatlab.org/nlab/show/symmetric+monoidal+category
http://nlab.mathforge.org/nlab/show/symmetric+monoidal+%28infinity%2C1%29-category
http://nlab.mathforge.org/nlab/show/compact+closed+category
nLab page on Symmetric monoidal category