Built-In ContentType and Field Ids
Only today that I've found that the WSS object model has 2 classes that hold all the IDs of the built-in ContentTypes and Fields.
Instead of doing things like this:
SPListItem item = list.Items.Add();
item["Title"] = "bla la bla";
You can do
item[SPBuiltInFieldId.Title] = "blab la bla";
For the fields you have SPBuiltInFieldId and for the content types SPBuiltInContentTypeId
:)