We have a Magformers set from Woot already. These are FANTASTIC. The neodymium magnets are strong enough to hold geometric constructions together - you can pick up the 'ball' shape without it falling apart, can't kick it though - and are very fun to snap together into different configurations. The magnets spin freely inside to orient themselves N-S as needed.
These are priced higher than a lot of other magnet toys, because the magnets are fully encased in plastic and cannot come out of the toy without obvious breakage. In other toys, it's possible for the magnets to pop out, and if your kid swallows a few they can die a horrible death of intestinal perforation.
Magformers don't have that issue. The magnet can't come out unless a piece is completely, obviously broken. I have 4 busy kids and they have not yet broken any of our Magformers. I feel that these are the safest magnet toy I've seen.