Is there a way to query for a list of custom records without knowing which custom records exist?

I'm not sure, but it looks like you can hit some of the backend stuff by changing the URL on a saved search. That seems like a good place to start. For example, I changed searchtype to "CustomRecord" and it exposed the ability to search within custom lists. Sorry it's not much of a help, but it might give you some hope! /app/common/search/search.nl?searchtype=CustomRecord&rectype=-1&cu=T&e=F

You can make a web services getCustomization call via script

@dansteg this looks promising.

ahhh......

var custSearch = search.create({

type: "customrecordtype",

filters: ['isinactive', 'is', false],

columns: ['scriptid', 'name']

});