All other industrial metals!
Other metals good investments? It depends on your investment time horizon. Everything will go up as supply tightens due to the cost of extraction, inflation or demand.
I personally have been stocking up on scrap copper and nickel. I've also been purchasing titanium in ingots from a local metal supply company. Why? Because they are all metals with industrial demand that is unlikely to wane, and they are EXTREMELY energy sensitive to extract or recycle which will effect the forward supply/demand balance.
The problem with the industrial metals is the premium for bullion. Copper bullion is ridiculously overpriced. My answer has been to stock the scrap, or ingots and will take them to the mint to produce rounds/bars if the economics ever dictate that course. Right now my local mint will produce rounds for $1.25/strike, less for large volumes. Still a high premium for the industrial metals, but maybe not in 15+ years.
Rare earths may turn out to be the play of the decade. The supply has not kept up with demand, but the downside here is a very small and inaccessible physical market. Producer stocks are pretty much the only way to play.
BTW, there are some really creative places to get your hands on some of these metals from scrap yards. I found ~100 lbs of nickel and titanium in scrapped jet engine compressor and turbine blades. Cashed in the copper from two AC compressors in 2007 when I upgraded them. The industrial metals are everywhere.
