You might want to think about planting some Dutch Iris bulbs. They bloom mid-May to the first of June or so for me and get me started nicely at my market. Vase life is longer than what most people are used to for Irises and you can plant a mix of different colors.

Also, try some Asiatic and Oriental lillies in the ground. I grow most of mine in crates but I also keep some in the field. Wonderfully perennial and great in bouquets.

Seed wise, if you are trying to plan for next season, don't forget to sow Larkspur this time of year. It will overwinter after it germinates.

Also, check out the cut flower forum on Garden Web. Lots of helpful folks over there.

Good Luck,
Carin