A recent article by CoinDesk [0] quotes the total number of listings on each of the biggest dark markets (before the seizures) and the number of listings for drugs; drugs made up a large majority of listings on all markets except Evolution, about half of whose listings are for drugs.

(The numbers come from a report [1] by the Digital Citizens Alliance; the report says the count is from January 2014, but says nothing further about methodology.)

The markets that sell weapons have significantly lower proportions of drug listings, so presumably many of the non-drug listings on those markets are for weapons; much of the rest is likely exploits, credit card numbers, forgeries, etc.

0. http://www.coindesk.com/dark-markets-grow-bigger-bolder-year...

1. https://media.gractions.com/314A5A5A9ABBBBC5E3BD824CF47C46EF... [PDF]