In general, coins do not make a very good investment medium. Solid collector coins, such as VF coins from the 1700-1800s, other than Morgan dollars, do retain their value quite well, and gain a bit of value hedging against inflation. Date rarity is more important than condition rarity for maintaining value. If you expect heavy inflation, these kinds of coins can keep you from losing money about as effectively as a good savings account, savings bonds or Treasury bonds. Remember though, that there may be substantial brokerage fees between buying and selling coins that can really eat into your potential profit. See our sections on selling coins and buying coins for the details.
Ultra-high grade or ultra-rare coins in the $20,000+ range (and some cheaper silver dollars) are termed "investor" coins. That's because they fluctuate in price more frequently than those coins with a substantial long-term collector basis for true value. Some people have made a lot of money on this stuff. Mostly coin dealers. Condition rarity can also put a coin into the "investor" realm. Be very careful about ultra-high grade (MS-68+) modern coinage, it can go up and down rapidly as well.
If you don't know a heck of a lot about coins, you will probably lose money investing in the rare coin market. Stick with more traditional investment mediums until you know more about the rare coin market.
My advice is to collect coins for fun. Learn about them. Never buy an expensive coin you don't know a lot about. Don't buy coins over the phone. Don't buy coins from advertisements you get in the mail with your bills. Finally, be wary of coin and bullion dealers who hock their wares as a "good investment".
If you learn a lot about coins, and exercise good judgement, then you probably won't lose too much money enjoying the Hobby of Kings.
If you are looking to buy coins for your collection or as an investment, American Coin can help. Buying coins successfully requires no more than a good knowledge of coins and the coins marketplace.
If you are looking to sell your coins and would like to better understand the coins marketplace and how best to sell, American Coin provides the tools and expertise to help you be successful.
If you are a beginning collector or investor looking for a great resource to learn about coins and coin collecting, American Coin is pleased to provide our online Coin School. On this site you can learn about identifying coins, grading coins for quality and value, finding the best channels for buying or selling, and much, much more.