sort(collect(Pkg.installed())) will print them in sorted order. show(STDOUT, "text/plain", sort(collect(Pkg.installed()))) will print them all, but it would be nice to have something better by default.
Are you using Windows? Julia’s package system currently uses lots of little files in the METADATA repo to store metadata, which is pretty slow on Windows (it was even worse before we switched to libgit in Julia 0.5). At some point we are hoping to switch to a new package metadata system that will eliminate this problem (https://github.com/JuliaLang/Juleps/blob/master/Pkg3.md).
Normally I would recommend looking at the listing at http://pkg.julialang.org/
To see the github listing directly you may have to clone the repo, or do print(readdir(Pkg.dir("METADATA"))) in Julia.
Normally if you do Pkg.checkout("somepackage"), then update() will stay on the master release. Is that not working?