BlackSheep,
You're right about central banks holding much of the world's gold. Even so: what they own, they can only sell once; whereas they can double the amount of fiat in existence again and again. I mentioned gold because the transaction and storage costs are lowest. Silver is a great alternative currency (for us poor men) since very little of it is held by large institutions. Currently the gold to silver ratio is a bit over 50:1, as compared with historical ratios closer to 20:1 or 15:1. I think the ratio has many reasons to close back towards historical levels (2 - 3 times rise in silver).
Like you said, central banks might dump their remaining gold in a last desperate effort to prop up their currencies. Furthermore, if the general public starts to distrust the currency and are looking to an alternative for every day use, then silver makes a lot more sense than gold. The tiniest gold coin of any practical use would be worth at least $50+ in today's terms. A silver "penny" (0.05 Oz T) on the other hand, is just small enough to buy the smallest typical purchases: candy bar, coffee, etc. and only slightly smaller than a current 10 cent piece. I would see demand for small denomination silver coins possibly increase dramatically in a fiat-money crisis.
As far as risk goes, I don't know. It kind of depends on your perspective. When the price of gold is fluctuating by 5 or 10 % from one week to the next, I really see it as the other way around; ie, confidence in fiat money fluctuating wildly up and down. Just having a few hundred dollars of money in my bank account or in paper makes me lose sleep at night! To me, it seems immoral (as much as it is unavoidable) to hold or deal with even small amounts of fiat money. I prefer not to do business with and support avowed criminals. 1-2% in a bank account sounds terrible. Inflation is closer to 15% or more, and could change unpredictably. And by having your money in a bank account, you are actually contributing to inflation!
As far as buying and selling gold or silver, I believe the USA is one of the best places in the world. You can get good prices through the internet (although not anonymous) or check out coin shows, and coins shops. Definitely check out different options for the best price. I think you should be able to do at least as well as 2-3% spread on gold (1oz fine) and 4-5% spread on silver (100oz fine). Smaller sizes will probably cost more like 7-10%, though. If you're planning on keeping them to spend directly in a fiat crisis, then "junk" silver (pre-1964 coins) can be a good idea. These can be bought for 5-10% below spot prices; although currently would cost you 15-20% to refine them, I can see them being accepted at par as money in the future.
I would really like to find some merchants around here that will sell their goods directly for silver. At least my drug dealer accepts silver! Other than that, I haven't really looked around; but the less fiat I have to touch, the happier I would be. 
When I spend paper, I really feel like I'm cheating the merchant, passing off a counterfeit note. Probably the more we can grow the silver economy, the better we'll be able to weather future government induced "business cycles".
Sorry to be off the topic of stocks. I still think stocks will do best in the long run, since they actually do generate returns in addition to capital gains. Look for highly capitalized stocks with the best dividends. Definitely don't chase after stocks that are just rising in price (like we all did in the 20's and 90's!) I'm just turned off by possible taxes, and having a paper trail. Maybe if you have enough money to pay the transaction costs, it would be worth looking for some tax haven to invest for you? I don't know how you would be able to smuggle your money back without being detected, though. Maybe something for a counter-economic entrepreneur to think about.
A-R.