I can't think of any cats that work well in a 10 gal. I have julii cory cats, which are smaller than a lot of cories reaching a max size of 1.5", but after observing their behaviors and activity levels in a larger tank they don't seem well suited to a tank quite that small. It's also hard to keep them in large enough groups. A lot of people do keep a pair in a 10 gal though. Every cat I can think of is supposed to be kept in groups..so I guess they really don't work great for a 10. The neons and pleco aren't the best fish for a 10 gal either. The neons really need more room for their natural schoaling behavoir, and should be kept in groups of 7 or more. The pleco I would be more concerned about though since a common pleco at it's mature size can require a 100+ gallon tank and they have a massive bio-load (lots of waste). There are some smaller type plecos so you may have one that is OK. If it is a common and you want to keep him, he'll have to be upgraded to a larger tank soon or taken to a lfs. If you want to keep the neons, get 2 more. If it's a common pleco, I think you are stocked/overstocked with him and the neons and shouldn't be adding more fish.
