Hello, and thanks for using JustAnswer.
A couple general tips. Clay soil has a pH of 7 to 8.5, so choose a plant with a similar tolerance. Also, try planting them with the rootball slightly above ground level, an inch or two perhaps. Typically, a flowering shrub that thrives in full sun will also tolerate soil with poor drainage, like what you are describing. I have a couple suggestions for you.
1. Hypericum Calycinum - St. John's Wort - Grows well in full sunlight and poor soil conditions. It has bright yellow flowers, about 3" diameter.
2. Rosa carolina - Carolina Rose - Pretty pink flowers, does real well in full sun
3. Potentilla fruticosa - Shrubby Cinquefoil - Similar to St. John's Wort, but smaller yellow flowers. Some varieties feature white, pink, or orange flowers.
4. Cephalanthus occidentalis - Buttonbush - Great for your needs, only downside is that bees like them because they are very fragrant
Many evergreen shrubs prefer slightly acidic soil. Your Cypress, though, does well in alkaline soils, and full sun. Probably the moisture is what caused them not to survive. They need well-drained soil. All of the above plants should do well for you.
I hope this information is helpful. If so, please click the "Accept" button. If you require further assistance, I will be happy to answer any follow up questions you may have.
Mark
Handyman
Done it all - carpentry, electrical, remodel - commercial & res. maintenance