Randall of xkcd has been having fun with data visualization lately. In his latest data-ish comic, Randall explores gravity wells. The height of each well is sized relative to the amount of energy (on Earth) it would take to escape that planet's gravity. The width of wells are scaled by planet size.
So you'd need one big arse rocket to escape Jupiter.
I know it's a comic, hand-drawn, and all stick-figurey and stuff, but Randall actually explains the concepts really well. There's good annotation, clear examples, and he's made an obscure topic easy to understand.
It's also entertaining in the Bill Nye the Science Guy (i.e. best Saturday morning show ever) sort of way.
[Thanks, Ricki and Thomas]