there are a number of good websites where you can sell your cards.
- Star City Games (or for that matter, any singles website you care to pick, there are literally hundreds) will buy cards at a lower than market price, instantly, with minimal fuss
- ebay will help you sell your cards but takes a sizeable cut.
- Magic Card Market for europeans is a good peer to peer selling platform
remember though, its not just rares that can be worth money, there are commons and uncommons that are worth more than many rares. wasteland, an uncommon, is worth around $60. Karakas, another uncommon is worth around $100, and mana drain, a third uncommon, is worth $172, there are also various commons, such as Serum Visions which is worth $3, or something like sinkhole, a $30 common. It is very much worth, if you are looking to get the best price for your cards, going through and finding the cards that are worth money, a quick way to do this is to print out a website's buy list and use it as a cheat sheet for cards that are worth money, if its on the list, you may well want to sell it individually, and you should set it aside (for now) and check its actual retail value (often three or more times what the buylist price is). if its lower than you want to bother with (its well worth setting yourself a limit, e.g. anything worth less than $1) sell it as bulk.
once you have set aside the cards you want to sell yourself, pick your favourite avenue, the returns you get depend on the time you want to invest. Sell the rest either as bulk collections on ebay, or to a singles website as they will often buy bulk.