Picked this tip up from the Intlaw listserv today: World Treaty Index from the Human Rights Education And Research Network . It is a test database so far.
I tested it by subject search. The subjects are coded, so you have to look at the table first to determine what subject you want from the list. For example, for treaties on legal subjects, select "9legal". If you fill in more than one search field, such as subject and party, both search conditions must be met (i.e. it treats it like a Boolean "and"). It is an InMagic DBText WebPublisher database which is what we use in my office. I found the word wheels to be a little slow at responding (a common WebPublisher problem or problem with the server?) . In the results, click on the treaty number for more details. As far as I can tell, links to the full text of treaties is not given although best bet for source is given. It does not appear to be comprehensive, but definitely has cites to a lot of treaties that otherwise might be inaccessible.