I've got a couple SGIs I picked up on a whim. As already stated, a lot of the vendors still charge a fortune for SGI parts. Craigslist and eBay are the places to get things on the cheap. Though, beware of location. Shipping can be expensive. Most SGI models are deceptively HEAVY!!!
Information is a bit sparse on the models, and there are a lot of variations. I don't have an O2, so I can't help you on specifics for it. Personally, I've always had a soft spot for the Indigo2 and Octane models, but probably because those were what I had the most exposure to at work early on. They are all really cool and unique systems. Personally, I'd love to have one of the massive Onyx Reality Engine machines, but I'd have to find one locally, as I wouldn't want to even dream of the shipping costs!
Obsolete has an
SGI Buyer's Guide you might want to check out. They have some helpful info for starting out, and a good overview for each of the common model lines.
