I'm currently working through bach's chorales and would like to do some more hymn reading as advocated by many to be the best thing for sight reading.

Which hymn books would you recommend?

If it's just for sight-reading, New English Hymnal or Common Praise. Or any hymn book really, except any of the Hymns Old and New stable which have many poor arrangements.

Agreed, Common Praise has some of the clearest printing to be found in any hymn book, and a number of less well known tunes. You could also explore hymn books from the Methodist and non-conformist traditions as they also contain tunes which are not found in Anglican hymn books.

There are also lots of chorale preludes for manuals only by composers such as J.G.Walther which you might like to explore.

I take it you mean organ sight reading? I use Hymns Old and New for vocal sightreading with very good results.

Thank you for the recommendations... it's for piano. I love the Bach chorales, but some of the intervals are a bit of a stretch in the left hand as they are after all written for singing.

So are hymn tunes.
Though useful I find that playing hymn tunes teaches you to play hymn tunes.
Most piano music is not like that.

If you're going for Methodist hymns, I'd try Hymns and Psalms rather than the new book, Singing the Faith - some of the arrangements in there are lovely, but contain page turns that are awkward enough when I'm turning for someone else and know the music, let alone sight reading! Also if you're looking for hymns (in voice parts) specifically then hymns and psalms has more.

The Little Flock Tune Book has heaps of traditional and old hymn tunes in four part harmony, but I don't know if it's widely available.