My oh my what to buy!
I think many of the modern coins seen today could be quite valuable in the future. I especially like Susan B's, Sacs Pennies, franklins and kennedy's along with MS Gold bullion eagles. Many of these coins in MS65+ in the raw can be bought for near face value through various sources.
My Key picks are 1980-1981(P/D/S) + 1999 Susan B in MS state
Sacagawea 2000-present (P/D)in MS
All years of franklin halves MS63+
Ikes especially 1971-73 in MS63+
Kennedy's up till 1987 in Ms66+
Pennies in MS65+
All Gold eagles MS68+ probably will take 30-60 years but could very well be the next set of Liberties or Gaudens
I myself put all of my spare cash into susan B's, franklins, MS gold eagles and liberties even though gold is outrageous I'm looking at the long term numistatic value. If you compare production numbers and look at similar coins from the 30's back you should be able to get an idea as to what has the potential to increase substancially in value. It would be awesome to take a $3.00 to $10.00 coin have it certified and hold 30-35 years till retirement only to discover its worth 5K plus. Now imagine 100 coins like that for retirement. Plus look at the fun finding these treasures now rather than years down the line.