Actually, the big
muff has been made by several
companies over the years. I'd tend to say the most common one you'll find these days is the Big Muff
Pi made by
Electro Harmonix. It's a great
pedal, it's got a nice crunchy fuzzy kinda sound. The downside is that it looks like it was built by a
russian tank manufacturer, which is pretty close to the truth actually. It's a huge industrial steel
green case with a button on the front, and a volume and
tone switch. It eats batteries like crazy too. But man, what tone!
You can also find schematics to build one on the web. The electronics can be bought for under $5, the most expensive part of the whole pedal is the battery. So if you like that sorta thing and don't feel like paying $50 for a used pedal, this might be a good option.