No one's mentioned sheep's crook and black dog yet. It is English trad isn't it? Also, not songs, but if you're interested in english folk you ought to have at least a brief look at some morris tunes etc.

Also I'd be tempted to add things like crazy man michael, however new they are, because they've become such an important part of the folk scene these days. Some of the more common cross-pollinations from ireland, scotland etc wouldn't go amiss either. Oh! and flondike shore I think it's called. Bloody good song. Where's Henry Martin from? And something dodgy like the cuckoo's nest. The whirly whorl is good too.