Electro-Harmonix came out with the Freeze back in 2010 and holy crap does it rule. It takes a split second of the signal from your guitar (or whatever), and perfectly sustains it for as long as you require. It allows for intuitive transition between chords, so if you are trying to fill up all of that space with all of that noise, you can do so easily. What's also neat about it is that it can capture all sorts of different timbres from your instrument, like if you click it on while you're pick scraping for instance, it sounds like a damn machine conveyer belt or something. Rad!
Coupled with other effects you can make fun new sounds too! With a POG (or any pitch shifting effect), you get some very convincing organ tones. There are tons of other applications, but anyways here's a few cool videos for you to check out. It's really simple to be honest, and it can really fill out your sound.