One of the more surprising developments over the past year has been the sheer amount of money spent in the collectibles industries. Just this past week two separate Michael Jordan "rookie" cards from the 1986 Fleer set sold for over $700,000 apiece (in perfect condition, mind you).
To put that in perspective, the same card (in the same condition) was selling for $40,000 back in March of last year. It's not just that card either, record sales are being made across the board when it comes to sports cards, leading some people to believe the market has evolved from just being a fun hobby to an entirely new "asset class" that can compete with stock trading and actual cold, hard specie like gold and silver.
So what should YOU do? Well, firstly, I'd take a look around to make sure you don't have any old sports cards (or trading cards in general) lying around unchecked. While most of the top sales consist of cards that have been professional graded, a lot of these cards were "common" to find in their era and are legitimately still sitting around in attics around the country (a quick look on ebay shows that even the most banged up/tossed-in-the-wash Jordan rookie card would still set one back four figures, so these are worth hunting-and-pecking for if you think you might have one).
While my personal expertise and interest is in sports cards, this uptick in interest has affected most of the collectibles markets, not limited to: comic books, retro video games, coins and money, records, stamps, etc...
So what can WE do for you? If you don't know where to start, it may be worth checking out various guides that can be easily requested through interlibrary loan. While the prices may be out of date with today's market, you can still get a good sense of what has some real worth and go from there.
Krause publishes various respected guides under their "Standard Catalog" series. For instance, those interested in old baseball cards should check their Standard Catalog of Vintage Baseball Cards, while those who want to review some particular old coins can check out their various guides on World or U.S. coins in different era. There are a multitude of different guides spanning many different interests in collecting. Beckett also releases various annual sports card price guides and are a big force within the industry. For comic book collectors, the annual Overstreet Comic Book Price Guide is an industry standard. The Scott Standard Postage Stamp Catalogue is a yearly go-to for stamp enthusiasts and collectors. While it is most helpful to have some of the recent publications, even older guides can help give some clarity to your collections and be a step in the right direction to evaluating what you have. Then, If you want to gauge the current market, you can always hop on over to ebay and check out what items have sold for (key word being "sold", not what items are being listed for - a good deal of obnoxiously priced items go unsold).
Perhaps you may unearth some treasure buried under some old clothes in the closest, or maybe it'll be hiding in plain sight right in front of your nose! Happy hunting!