Shawn you can plant most anything in a barrel like that, it just depends whether you want to do perrenials and have them return every year or whether you want to try new things every year.
I have 2 in my front yard and I do annuals in them because I like to change plants for the seasons.
I usually do impatiens with some ivy around the edges, sometimes million bells whatever strikes my fancy at the garden store and will do well where the barrels are located.
In the fall I switch over to mums and tuck in small pumpkins and hang indian corn on the front.
Winter I put small holly or mini pine trees etc.