Chocolate Soldier - the darkest red single peony I know, dependable grower and bloomer, very hard to get (in fact, if you know of a good address for purchasing, please let me know)
Henry Bockstoce - the tallest fullest red around. Very bright red and massive plant display. Thumb-thick stems, huge flowers, very high habitat. Possibly the latest blooming true red peony.
Amabilis - beautiful pink. High flower production. Very common in Holland.

Here is a link that might be useful: Peony information and catalogue of quality peonies