The Lasso Page is maintained by the inventor of lasso and provides most important references for lasso.

The book *Elements of Statistical Learning* (pdf) describes the lasso in detail.

Lasso in R: lars: Least Angle Regression, Lasso and Forward Stagewise, and glmnet: Lasso and elastic-net regularized generalized linear models (Note: lars() function from the lars package is probably much slower than glmnet() from glmnet.)

Adaptive lasso in R

adaptive.lasso function in lqa package (Penalized Likelihood Inference for GLMs)

adalasso function in parcor package (Regularized estimation of partial correlation matrices)

Graphical lasso in R (glasso: Graphical lasso- estimation of Gaussian graphical models)

The joint graphical lasso paper

Joint graphical lasso in R (JGL: Performs the Joint Graphical Lasso for sparse inverse covariance estimation on multiple classes)