If you are using InfoPath 2010 / SharePoint 2010, you may have already realized you can create REST connections that leverage SharePoint's OData service (ListData.svc). And while there is great documentation on the OData URI protocol conventions, I found an amazing (and gorgeous! H-o-t-!) OData browser today. Check it out here - it is called the Sesame Data Browser, and it will make figuring out those queries so much easier.