Word on the street is that coins under $5000 are doing great. Avoid "medals" that have no face value most of the time. The only exceptions that I have seen are some key date medals, which I will mention later. Gold has usually performed better than silver, but interest in silver seems to be increasing, especially outside China. For now, I suggest sticking with gold. Palladium has become very popular in China, but I don't know how long that will last. Gold is always popular.
The top key coins seem to have slowed down now that they're all in the 5 figure range of $10000 or more. Few people can afford to drive prices up further on those coins at that price level, so while they're still a great investment, they haven't been performing as well as coins under $5000 in the short term. Over the long term, the rarest coins are the safest investment bet because, even though they may have slowed down lately, they are still steady gainers with ready buyers at all times.
Here's some specific suggestions to get you started, with mintages and estimated prices for NGC PF69 specimens:
1995 1 oz gold proof panda (mintage: 555, price: $9000)
1995 1 oz gold unicorn (mintage: 504, price: $8000)
1993 1 oz gold fu, lu, shu (mintage: 303, price: $13000)
1993 1 oz gold peacock (mintage: 1200, price: $8000)
2000 1/2 oz gold scallop dragon (mintage: 2300, price: $2800)
1988 1 oz gold "AU" non-error basel panda medal (mintage: 400, price: $3000)
1988 1 oz gold "PT" error basel panda medal (mintage: 600, price: $2500)
1985 1 oz silver 94th ANA Convention "GREAT WALL OF CHINA" backwards error medal (mintage: 500, price: $1000+?)
1995 or earlier NGC PF70 or PCGS PR70 popular key gold coins
Always buy coins that have been authenticated and graded by NGC or PCGS, with a grade of at least 69 (out of 70). Resist the temptation to buy ungraded "bargain" coins. The best investment coins will probably cost you the highest price ever paid for the coin, but don't worry about it. Just get it for whatever the best price is that you have to pay, and enjoy the onslaught of buyers begging you to sell it to them! Make sure you buy from a reputable seller, and avoid buying on ebay if you can buy direct from the dealer instead.
That last one about the PF70 and PR70 coins is my latest secret trick, but I think it's OK for me to share it since those coins are so incredibly rare. There's probably only around 20 to 50 of them TOTAL, in all dates and all types, from 1995 and earlier. You can expect to pay truly ridiculous prices for those coins when you buy, and you can also expect to be paid truly ridiculous prices when you sell.
There are several other great investment coins that I could recommend, but I'd like to keep them secret until I'm able to find specimens for myself. I wouldn't want to have to bid against my own proteges.
