According to Cool Tools, the best source for Neodymium Iron Boron (NIB) super magnets is "Mr. George the SuperMagnetMan." He's a charming fellow, wont to saying things like, "These magnets have caused more blood blisters than any other magnet I have."
His prices are the best on the net. His selection is vast: no one else has the stock he has or the variations in size of commonly available shapes. This is no exaggeration or hype. He's got stuff you can't get anywhere else and is constantly adding new items, like axially- and diametrically-magnetized NIB wedding rings and radially-magnetized ring magnets. He has magnets so large they are dangerous (fortunately he has put videos on YouTube that show you how to safely handle these monsters — with large leather welding gloves and a special wooden wedge and a 2×4!). He also sells magnetic hooks, pyramid shaped magnets, magnetic jewelry, teflon coated magnets, heart, star, and triangle magnets. You can even get powdered magnets that act like iron filings on steroids! You name it he's got it. Most magnets are N45-N50 grade, the highest strength you can buy.
Don't miss Mr. George's video of supermagnet crashes, where he smashes limes and grapes.