Hi, Peter - The best MacColl CD I've seen is a 20-cut collection called Black and White - Ewan MacColl, The Definitive Collection (click here). This is a collection of songs MacColl wrote himself. It doesn't seem to be available at the online stores like CDNOW, but Green Linnet still has it listed, and you can order direct if you follow the link.
Tradition has two excellent reissues (and at budget prices):
"Classic Scots Ballads," by MacColl & Peggy Seeger
"Blow Boys, Blow," by MacColl and A.L. Lloyd
There's also a "75th Birthday Symposium" CD with 11 songs and an interview, but most of the songs are on the "Black & White" CD (I haven't heard this 75th birthday CD, or the Topic CD called "Real MacColl.")
-Joe Offer-