The 2009 redbook is a pretty good place to start for numismatic values and to see what coinage is available. For graded coins with no problems I like to use the Fair market Value
as a guide to what each grade tops out at to some collectors, though even on ebay you will find people bid both higher and lower on certain coins.... after all it is an auction. grading coins cadds additional cost to a coin, like around $50, so some of the coinsage you get under that value for collectable coins is worth the pricetag as values are usually not disputed......
for just average coinage which has little value but melt, I like to check the buy price at Kitco refining
and a person has to remeber to figure in shipping on those coins both ways if buying online, or even cost of driving downtown to a coin shop..... On Friday 14-Nov-2008 Kitco was paying $6.00 per dollar face on pre 1964 coinage, which is just a little lower than spot price for most coins.... an example would be that a pre 1964 quarter has a melt value of $1.72 and Kitco would pay $1.50 delivered to them for each quarter [you generally need to have a few ounces to deal with folks who refine, though you can sell to a broker who will give somewhat a fair price, but we have to ship too]
Currently the Silver coin production is limited to silver eagles and to silver proof coins available from the US Mint online store
for quite a bit higher than market spot price, but a person can still get the special mint issues which have higher collector value. Gold eagles and Gold buffalo's and other gold coins are still available too, though one never knows whent hey will pull the coins or run out of stock on some issues. there is some good last chance products that went up this weekend from years past that have high value, though not all are silver or gold.
If you buy coins, get to a reputable dealer, ask questions, go to another dealer if you can and verify what you learned, quite a few coin dealers can be found in advertisments of coin magazines, get to the magazine section of your favorite store and peruse the titles, I like Coins by Krause publications
mostly because they publish a list of values each month, though a little behind the grey sheet and other weekly dealer lists.... and they publish "The Gun List" too along with some other magazines on collectibles.
coinage is a great investment, most older silver dolars preformed better than 12% over the past year without losing in the recent downturn of the spot market, or the downwrds spiral of the stock market either..... many folks are seeking out quality coins as an investment for the long term gain now, and I personally think it is a wide idea in the volitile market condidtions folks are experiencing. Purchase the highest quality coins you can afford instead of the lower quality coins and buying more, for over the long term [20 years] those higher quality coins gain better in value and the lower quality ones thought hey gain do not preform as well.... though still sought after by new collectors filling slots in collections. ergo, purchasing MS70 and PR70 graded coins is a good thing, if you look on a place like ebay, you will find in a search for grading services like PCGS, ANACS, NGC, and ICG you will pull up many quality cons, and that the higher grade coins go for obvious higher pricetags.... PCGS price Guide
you will find higher dollar values but it only applies to PCGS coins, some collectors will not purchase anything else.... I trade any holder as i buy the coin and not the holder...... I also buy non-graded coins but have got burned on a few here and there, a recently purchased a 1914-D buffalo nickel for my son's collection only to find it was the more rare 1914-S but an acid date and it was not described as such, just offered with a no reserve bid on ebay.... The fella offered my money back, but as a place holder it was still worth the $5 I paid for it, and i was happy that the bid did not go higher, but my 8 year old is disappointed [Note to anyone that has a few old coins laying around, or an estate collection even, I may be interested in what you have too, PM me and we can haggle]
I have more information if anyone needs or wants, many coin sites and clubs around the world to look into, it is a fascinating hobby and business to be in, as a person meets a cross section of people they would not normally think they would meet, from all walks of life come those who appreciate the beauty and value of collectible coins.