There is a web site www.historictrees.org Then click on store...... This site offers seedling trees that have an link or association to historic people (presidents etc) or sites.. There is a seedling from the "Lincoln Oak". for example. This might give a list of interisting trees & give a "different" approach to your park.... By the way this was thought was used and 14 trees were selected to be included in the garden by the railroad station where Lincoln left springfield Il. (to become President) & returned after his death. It is also in sight of the New Lincoln Presidental Library.......

I have not found Abies to to very well here and have also felt the heat was a factor.

My first suggestion is for you to define what constitutes "highly decorative". Then there are the usual important considerations, like how much space is available, what region is the planting site in, what are the soil and exposure, what else is present in the scene with which the new tree(s) is supposed to look good...

One of my favorite ornamentals is the Yoshino Cherry (Prunus Yeodonis). Eye catching white blossoms in spring and good foliage during the growing season. In the fall they tend to have a yellow-gold leaf color.

Any of the redbuds might be good or Japanese maples. Of course it all depends on your location and how large of a tree you want to use, as others have said. You've got lots of options.