A report just out tallies all the new species for 2007: 18,516. Over 75% were invertebrates, while 11 percent were plants and 6.7 percent were vertebrates.
The report from the International Institute for Species Exploration at Arizona State University also named a "Top 10" new species from 2008 (total numbers for the year are still being tallied.) They include a palm tree that dies when it flowers (it's humbling to think we don't even know how many kinds of trees live on this planet), the world's longest insect, the world's smallest snake (both described earlier in this blog), one fossil species (a fish preserved in the act of giving birth) and extremeophile bacteria surviving in hairspray.
COMMENT: The conceit that we know all the species, or at least all the vertebrate animals, on Earth, takes new hits every year. Still, if a poll was taken, I suspect the average citizen would presume we knew all the vertebrates.