If you become a numismatist (collector of coins, paper money, tokens and medals), you should decide if your primary focus is on collecting, investing, or a combination of the two.  Collectibles are a much different kind of investment than stocks and bonds.  Collectibles do not produce monetary interest or dividends; they have value only because of limited supply combined with demand from collectors who appreciate their historical, artistic or other merits.  Numismatic items tend to gain in value when there is more money to be spent (either because of inflation or because of greater wealth) or when there is an increase in popularity (as we are seeing now with the 50 State Quarters and the Sacagawea dollar).

Recent history of coin supply/demand trends:

1960's — Coin collecting very popular with well-attended club meetings, but fairly narrow focus on modern U.S. coins.

1970's — Collecting U.S. coins by design type becomes popular; prices increase due to inflation and rising price of silver and gold.  Price of silver peaks at about $50/ounce in 1980 before falling rapidly.

1980's — introduction of third-party graded coins encapsulated in plastic "slabs"; temporary speculative price increases for many high quality (but not necessarily rare) "slabbed" coins.

1990's — numismatic investments perform much worse than the stock market; coin prices fairly flat (often well below 1980's peak values); coin collecting and other "old-time" hobbies suffer due to increasing demands for peoples' time.

Late 1990's — resurgence of interest in coins due to new U.S. coin designs; prices on high-end material increase due to wealthy bidders (many of whom made their money in the stock market).  Internet auctions pioneered by eBay® make it much easier to buy and sell collectibles, including numismatic items.

2000 to date — although the decade got off to a rocky start with the "dot com" and stock market downturns and the attacks of September 11, 2001, the economic picture improved significantly in 2004 and 2005. Collector interest remains high in many areas, with strong prices realized (including new price records) at major numismatic auctions! The prices of silver and gold are also at their highest levels since about 1980.

The best advice here for the average person is probably to enjoy collecting, treat it as a hobby, and spend only a modest amount of money. Coin investing has many risks (for example, coins are not a standard commodity and are subject to differences of opinion with regard to grade and value) and should be approached with great caution, and only when the investor possesses the necessary knowledge. You can gain a great deal of knowledge and fellowship by joining a coin club and becoming friends with experienced members who specialize in various aspects of numismatics.