[waxjar]

I just use a piece of paper.

For coding I use comments and a git alias (git todo) that returns the comments.

    todo     = !git grep --color=always --no-index --exclude-standard --heading --break --ignore-case -e ' FIX: *' -e ' TODO: *' | sed -e 's/^[[:space:]]*//'

Long term stuff I keep in Notational Velocity, among a load of other things.