I think it was a bit unfair to called Thyra a "drama queen". A fair point was made there.
Fishman, I really think you have quite a nice mix of fish right now. Why upset the balance? I'd personally let things settle for a while and make sure all's going well and maintains this way before rushing to buy another fish.
Newman, and everyone else, is spot on about the spotted raphael cat. Great fish but not a good fish for a 20 gallon. What you're forgetting here is that you're tank is a 20g TALL not long, there's not that much floor space for three boisterous cats to share. It's not a case of "what would one more fish do", it all depends what fish that is.
Also the above 3 or so posters that mentioned it chomping on your other fish are very correct, it'd be a total waste of money if your danios and cherry barbs got eaten and you'd only want to replace them with something else. Also, as I've said before your tank is quite sparse, to even consider another bottom feeder you need to up the plants and decoration and get some more hiding places in there.
Basically, you do have space for another fish or 2, but I honestly don't think a spotted raphael is the way to go, it's too risky for a number of reasons all listed in the above posts. For a bigger thank in the future, possibly.
Sometimes you need to stop thinking about what would be "cool" and what fish instantly draws you and start thinking PRACTICALLY about what fish would actually suit your current set-up, and leave those dream fish until you can accommodate them. We all have to at times.
I know, long post, please read it and the above carefully and really consider what we say. Only looking out for you and your fish at the end of the day. As Thyra rightly said, there's not much point asking if you're not prepared to change your mind if you don't get the answer you were hoping for.
*Goes back to sleep
*