There are many fish that are compatible with neons. Many of the smaller/medium sized tetras will work (just avoid tetras like congos.. they grow too large for a 45 gal). You could try a pair of angelfish... though get them when their young. If you get angelfish when they're young, there's a good chance that they won't prey on the neons as they grow up, because by the time they get large enough to eat a juv. neon, the neons in the tank should have grown up. Cory cats would work well if you want some movement on your substrate. There are so many possibilities... I'd suggest going window shopping at your LFS. Write down what sort of fish you'd like to keep, then get back to us on it.
I forget what kind of plants can grow up enough to provide surface cover, however most stem plants should do the trick. Personally, I would suggest using floating plants. Unless you can get a well grown out plant, most of the plants you get from a LFS would not be tall enough to reach the surface of your tank. During the time that it would take the plant to grow large enough, you'll be battling algae blooms. I'll see if I can get a picture of my plant tank now... its quite a bit overgrown and some of the stem plants in there are shading out the tank. It'll give you an idea whether or not you like the look. On a personal level, I don't like seeing my plants reach the surface of the tank... I usually keep them trimmed a couple of inches from the surface. So if I needed surface cover, I would use floating plants.
Try out other freshwater boards if you want help from someone other than me. There are so many ways to go around planting a tank, that no one person is correct. I believe that
www.plantgeek.com is quite a decent aquatic plant site. Other FW boards like
www.aquariacentral.com have a few experienced plant keepers as well.
HTH
-Richer