I'm a huge comic collector, mainly Spider-Man and other Marvel characters. I've been collecting and reading comic since I was 10, I'm now almost 30. Have a good friend who runs a comic book store in Brandon check it out sometime if your in the area Readmorecomics.com sorry for the shameless plug.
My collection mostly consist of Amazing Spider-Man back issues I have every issues from #17-670 (the current issue), missing 10 of the earlier issues to complete my collection.
Nicodemus-Back issues are not much of a market these days. Most of the time if you are going to try and sell anything you won't get market price for it, at best if you sell to a shop you'll get a 3rd of the value. That said you may get the price you want on Ebay, but with both Marvel and DC rebooting their franchises you may find that the price slumps even further.
Wrong, back issues are very much in demand do a quick Ebay search, and see how much even low grade copies of Amazing Fantasy #15 (1st Spider-Man), Hulk #181 (1st Wolverine) and other Marvel classics from the 60's and 70's. Of course if you sell a comic to a store you aren't going to get megabucks for it as they need to sell it for a profit and know telling how long it will take up space in their shop. Yes, DC has recently rebooted and renumbered all their titles but Marvel is not doing this gimmick. They every so often renumber their titles to attract new readers or to coincide with a movie release for example both Captain America and Thor relaunched with new #1 series to coincide with the releases of their movies. Renumbered titles don't effect the cost of back issues.
Typically comics from the 60's and earlier are the comics worth the most amount of money. Action Comics #1 first appearance of Superman, Detective Comics #27 1st Batman and Amazing Fantasy #15 1st Spider-Man are the 3 most sought after comics and have all been sold at auction for over a million each in NM condition. If you are looking to get the max for your comics look into a service called CGC. They proffessional grade and seal comics, the previous mentioned comics all sold for over a million by being proffessionally graded. Very few comics from the 70's onward are deemed vaulable to collectors. Incredible Hulk #181 1st appearance of Wolverine and Amazing Spider-Man #300 1st appearance of Venom are pretty valuable depending on their condition.
Modern comics (1980-current) have very little high dollar value. There are a few titles from Independent Publishers like Image or Vertigo that are valued at $100 or over such as Walking Dead #1. If your getting into the hobby for financial reasons your getting into it for the wrong reasons. Unless your luck and find a few Silver Age (comics from the 60's and 70's) gems at a garage sale or in a relative's home.
Welcome to the hobby.
Well I did say that you might get the price you want on Ebay.

I collected comics as a hobby late 70's-80's-90s and stopped when the stores over here stopped selling back issues. Most of the fun is browsing through a shops back issues to see if you can find a gem. When most of the stores in the UK stopped stocking back issues and only sold recent releases it took half the fun out of it. These days I have gone from buying the comics themselves to buying the original comic art. It has brought back the fun of hunting for a gem again, that said I've probably got a few thousand comics that I really must go through and catalogue at some stage. Would I sell them, probably not, the stories are still great and hopefully one day (when I have kids) I can share them with with a new generation. The original comic art will be my own guilty little pleasure kept away from the Mrs in the meantime.