Catalan is a co-official language along with Spanish in the region on the Eastern edge of Spain. It uses the same alphabet as Spanish except it has no ñ and adds the digraph l·l (ela geminada).
OS X 10.3 had a Catalan keyboard layout which was identical to Spanish-ISO except for the flag icon. This seems to be no longer present in my 10.4. From my iDisk you can download the Catalan folder, which contains the .keylayout file and the .icns file with the right flag. The layout is almost the same as Spanish-ISO. The middle dot · (U+00B7) which is the standard for producing l·l is at shift + 3. But also included are ŀ (U+0140) and Ŀ (U+013F) at option + o and option + shift + o, in case you want to use these versions for local printing or similar purposes.