If you haven't heard it, there's an audio tape you can get called 'By Heart: 101 Poems to Remember.' It has an introduction with him talking about what he thinks the best ways are to memorise a poem, then he reads 101 poems (not his, there's a brilliant mixture of stuff on there). It's really worth it - is 2 tapes and he has such a great voice for reading poetry. I think there's a book of it, too, but the tape would be better. I don't think it's on the US Amazon site.
I was surprised the first time I heard him reading because he sounded a lot 'smaller' somehow than I had thought he would. He sounds so different from what I imagine, like here: http://www.bbc.co.uk/arts/poetry/outloud/hughes.shtml
(you need realplayer) to hear that I think.
There's a clip here: http://www.youtube.com/watch?v=o8kvmXvR1pU
of Frieda Hughes accepting the Whitbread award for 'Birthday Letters' the year after he died. The bit of his letter she reads is interesting.