This is a great video showing many different possibilities of manipulating coins with strong magnets:
You also notice at the end of the video it is also possible to stop certain cell phones and note that the same applies to wristwatches.
Obtaining strong earth magnets (neodynium magnets) can be done on e-bay and I highly recommend it to anyone that are interested to perform this kind of magic trick.
One great thing I found when playing with my own magnets is that some plastic looking poker chips do have metal inside and can be manipulated through a table using a magnet (usually put in my sock). I got a few people freaked out with this one
The size of the magnet I recommend is the size of a magician’s M5 (2″x2″) but 1″ by 1″ will suffice to manipulate a quarter through some but not all tables, it will be enough to make the coin stand up through your hand however.
If you’re in the USA or somewhere coins are not attracted to magnets you will need to buy a fake one that will stick to a magnet.