so you have a Lyretail Lamprologus and a Hemichromis bimaculatus in a 10 gal tank right? there are a few problems with this and thats size and compatability. seeing as you plan to buy the biggest tank you can the size wont be a problem. if you have the cash spring for a 125 gal tank, his gives you lots of options further down the line if you decide you'd like a change.
the two fish you have are not ideally suited as tank mates they come from diffrent regions and each prefer diffrent PH of water the 'fairy' likes a high ph of around 8.5 and the 'jewel' like s a lower ph neaer 6.5/7 its not really the done thing to mix fish from diffrent regions and i believe this is because fish use shapes to identify each other and it is related to the subtle diffrences in the two fish. to be honest no matter how much the guy at the fish shop 'likes you' im thinking by the fish hes already sold you, he prefers your purse.... either that or you havnt told him what you already own and the tank size.
the good news is that you are here trying to find out what would be suitable for your next addition to the tank so for that you have learned something from our forays of recent times.
my advice, and as ever you are welcome to ignore it or take it on board here, is: to choose one of the two you already have and stick with that type. seeing as the jewels can be overtly aggressive (i have two and they are evil) i would probably go with the 'fairy' this fish is from a group that live in an african lake called tanganiyka so they are known as tanganikan cichlids. they are great to keep but as i said earlier they do benifit from a high PH (do you know what the PH of your water is at home?) i think this should be the deciding factor. do a bit of research on the web for tanginiykan cichlids and see what comes up. although you may find it hard to get much choice at your LFS.
if you really want a nice colourful tank then many like to keep malawi cichlids, again these a re a type of cichlids from a lake called malawi, also in africa. but dont be fooled that because they are from the same area means they are safe with each other, you still need to ask and read to double check.
another option and this one is my favorite, is south american cicghlids. most of these tand to be larger so a 125 gal tank, although OK, would be better as a 200 gal. i prefer south american stuff and i would suspect in america you'd have no trouble getting hold of almost anything. take a look at some of the 'geophagus' 'uarus' 'hero notatus' or 'threadfin acaras' these are trully stunning fish to look at and enjoy. heres the begining of my tank.
i hope my answer has taught you some of the basics to help you choose you fish.
oh man i love steak too!!