Harlock,
The only fish I have had experience keeping the rams with are neon dwarf gourami, danios and otocinclus. They seem to get along fine with all of these fish....but I did have one in with a female betta for a short time while I waited to set up another tank for it. It didn't do well with the betta. I believe they need to be with other peaceful fish. Mine was all stressed out when the betta kept pestering her.
They do tend to aggression towards each other as they settle property disputes. I had 1 male and 3 females in a 29 gallon and I had to take 2 female out when the male decided which babe he wanted to shack up with...lol...the two of them kept chasing and harrassing the other two until thier colors faded and they were pretty unhappy. I have read that a pair need no less than 2ft of space for thier territory, though you could put one in a smaller tank.
I love these little fish Harlock..they are just beautiful and have a neat personality for a fish. I haven't had any trouble keeping them at all...but I did have an issue with cammallanus nematodes on 3 that I bought from one batch. ONe died but the other two are doing well. None of my other fish have been affected.
I have read that corys are a problem for these rams, especially if you have a pair breeding. The corys get in thier space and annoy them from what I have read from others.
Do get some Harlock, they're great ! I have alot of little babies I'm going to need to find homes for in a few months.....but shipping is expensive !

I do have an LFS who will take them though...