This R command lists all the packages installed by the user (ignoring packages that come with R such as base and foreign) and the package versions.
Package Version bitops 1.0-6 BradleyTerry2 1.0-6 brew 1.0-6 brglm 0.5-9 car 2.0-25 caret 6.0-47 coin 1.0-24 colorspace 1.2-6 crayon 1.2.1 devtools 1.8.0 dichromat 2.0-0 digest 0.6.8 earth 4.4.0 evaluate 0.7 [..snip..]
Tested with R 3.2.0.
This is a small step towards managing package versions: for a better solution, see the checkpoint package. You could also use the first column to reinstall user-installed R packages after an R upgrade.