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I know you mentioned the ghost shrimp, but what about either RCS (red cherry shrimp) or CRS (crystal red shrimp? They are more colorful and neat to watch. Chances are you probably would have limited reproduction because the guppies would fine the babies quite tasty, but you can often find the RCS at a decent price from local aquariusts. A dozen wouldn't be too many to start out with. You could even try 1/2 a dozen of each because they can't interbreed and neither will breed with the ghost shrimp either.
There are some pretty platies out there, but they prefer cooler, unheated water where as the other species you have like a little warmth. There are some nice Endlers' livebearers and their hybrids that come in a huge color variety. Another idea is some of the smaller Rasboras, which are mostly in the red/orange color. Corydorus pygmeasus are a schooling Cory, but they prefer midwater and have a neat behavior. They aren't very colorful though. If it were my tank I would get 1/2 dozen CRS (or CBS crystal black shrimp) and 1//2 dozen RCS (expecting that not all will make it) and a couple pairs of Endlers'. Keep in mind that the guppies can interbreed with the Endlers', but who knows what fun crosses will show up.
Be careful in stocking. The more you put in there, the more you have to feed, the more they will poo, the more excess nutrients, the more need to do more water changes or the more the algae will grow. You are already fighting an imbalance by the sounds of the algae you're dealing with. Any time you add or remove anything from a small ecosystem like and aquarium (especially a small volume like a 10 gallon) the balance is thrown out of whack easily. You'll need to go with the flow and adjust your maintenance to the signs your tank is telling you. Over the years I've gotten lazy and discovered that live plants, when there is enough of them that grow at a fast rate, can cut down on tank maintenance dramatically. There is a learning curve to live plants, granted, but once you get the hang of it, its easier and healthier (little to no nitrogen cycle), the fish are more at ease and, personally, I think it looks much more pleasing to the eye. To top it off, its fun to share plant trimmings with others. And yes, its possible to have lush growth with nothing more than a compact florescent light in a 10 gallon and no CO2, you do have you fertilize and there are some tricks, but live plants don't have to be an expensive ordeal. If anyone is interested I can take some pics and post them to give an idea.