The Internet Assigned Numbers Authority is in charge of doling out IP address blocks. Last Friday, June 17th 2005, five previously unused /8 netblocks (same size as a class A network, aka 16 million addresses) were allocated.
Three netblocks went to North America via the American Registry for Internet Numbers.
Two netblocks went to Latin America and the Caribbean via the Latin America and Caribbean Internet Addresses Registry.
If you filter bogons on your firewall, update your filters accordingly.