I don't know if this falls in the "gear and recording" section, but here goes...
My asshole neighbors aparently don't like metal or hardcore, the PIGS have
been called on me around 7 times in the past 2 mo., I just upgraded my half stack to 3/4 stack, my ampeg head blew so I purchased a Randall rg100sc,
w/ external speaker jacks, 100w@ 8 ohms, 150w@ 4 ohms, it pushes my 4x12
cab w/ ease. Anyway, I need some advice on cheap but good sound proofing
materials, maybee egg cartons? I don't know. any help would be great!

If you're gonna push a 100w head to near its max, a few egg cartons aren't gonna do the trick... with soundproofing, you really have to put the money in to reap the rewards. Start by moving your amp nearer the middle of the room, and put it on some carpet if its on wood, then deal with any windows/air vents. Hanging some carpet from the ceiling to the floor, but a little way from the wall will help, good luck!

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To completely "soundproof" you have to build a second wall inside your current walls, leaving space in between. This helps prevent the sound vibrations from traveling through the walls and into your neighbors ears. Also, egg cartons are primarily for improving acoustics.

Cheers.

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kill your neighbours.

I recomend using a bat

yea fuck ur neighbors to hell, mine are like that too rich bastards.
ive seen that wood you buy at home depot to put up in your garage to hang stuff on work. dark brown wood with lots of holes. the padding that you put on your bed that looks like egg carton works pretty well, put cocking around your windows if thers gaps or carpet on the walls will work pretty good too like the guy said earlier