There isn't yet a Strunk and White for URI design, but the recent book RESTful Web Services, by Sam Ruby and Leonard Richardson, does touch on the subject.

For example, they recommend that when you are designing URIs, you should use forward slashes to encode hierarchy (/parent/child), commas to encode ordered siblings (/parent/child1,child2), and semicolons to encode unordered siblings (/parent/red;green).