It depends on what you are looking for:
If you want something very slow with a lot of body control, go for something like colors, by amos lee, Jordin Sparks new stuff, or something from idina menzel that's not from a musical.
If you want something with a truly deep meaning, you might try James Morrison, Linda Eder, or Josh Groban. They all have some really deep songs. Now Comes the Night is another great one from Rob Thomas.
If you want something a little more upbeat, try Back at Your Door by Maroon 5, Little Wonders by Rob Thomas, or any of the past American Idol winners. A lot of their demo CDs have some great songs to choose from.
I hope this helps! I did a solo once, and it took me forever to choose. I ended up using Diana Degarmo's Emotional, and it was one of everyone's favorite dances at recital. Good Luck!