I am so sorry for your loss. And a memorial garden is a lovely way to honor your son. Hummingbirds like red flowers. You can find red honeysuckle vines, red trumpet flower vines to train up a trellis behind the bench or an arch over the bench. Hang a couple of feeders as well. A grassy area, with a stepping stone path to the bench would be pretty. If you are feeling up to it, and have the space, a marsh garden or pond at the low spot that collects rain water would add to the tranquility. You can google to find out how to make and maintain the marsh or wetlands garden.

Thank you so much for the great ideas. Already have the hummingbird feeders up and have actually seen one. Also put up a hummingbird house hoping at some point to have them come and live there.

I think your memorial garden is a wonderful idea. You didn't mention what zone you are in, but I had very good luck with black and blue salvia. The hummingbirds really liked it, it tolerated our extreme Midwest conditions, and the blooms are a masculine dark blue and purple. It won't like being in a bog, but perhaps it might work for you on the drier fringes of your garden. Best of luck!

Thank you for your suggestion...I am in Northern Kentucky

Celeste, I am sorry for your loss. I found this link that might help you find the right perennials.
http://www.gardenguides.com/91275-perennial-marsh-plants.html