What kind of fish do you like? Why do you care what we would do?
I'd possibly do a Lake Tanganyika tank, or a planted Amazon tank.
Within the next 6-8 months or maybe a little sooner, I'll have the same predicament. I'm upgrading most of the fish in my 75 gallon to a 120, and now I'm mulling over what to do with the 75. On the one hand, I could use it to continue to grow out my ornate longer, but I'm really leaning towards a SE Asian biotope for my clowns to grow out in a few more years till they need a bigger tank.
I'm thinking of getting a little bit more cork bark, doing a cork bark background that I can grow java moss and java fern on, trying to find another bigger piece or two of nice Malaysian driftwood. I also plan on trying out some patches of crypts here and there and maybe some other Asian plants.
For stocking, I'm thinking my 5 clowns as well as maybe another 2-3 4" or smaller clowns. Then another couple species of small loaches that can stay in the tank after the clowns have to move out, maybe a couple kuhli species and/or sids. Then I'll have a few gouramis, SAEs, and fill out the rest of the tank with barbs or rasboras.