What do you guys do about getting big fat booming bass sound? It's so important.

I have had good results with the Lizard2 synth. I just can't get that same sound out of my own bass guitar!!

BTW, I have had really good luck replicating an upright bass sound by recording my acoustic guitar and pitch shifting it down two octaves in Ableton. Then I add Bassxpander which fattens the whole thing up.
That doesn't give the type of sound I'm talking about, but it sure sounds cool.