Honestly, I think that aquaria are good for fish and that reptiles require a different setup. Not that you can't make an aquarium work, I have in the past, its just there are better alternatives.
I would also not base my jundgement of what is best for me on what I can keep in the cage I have available. Sure that empty cage syndrome has grabbed all of us, but I think you will be better off choosing what you want, and building or madifing a cage around that species.
Look through some book, do some googling, go to the library, anything to expose yourself to the variety of herps available. I would than catorgize what you desire out of a herp into the animals you find of interest, things like, ease of care, the ability to achieve the proper enviroment, size, food requirements.
By analyzing all the factors you will come up with the animal that suits you. Or maybe there is a particualr species that you are just fasinated with. I myself am infactuated with Red Tail boas and Green Tree Monitors. I don't have the experience to keep the latter but am gaining that experiance by keeping bearded dragons and hopefully in the near future Ackies.
If I had a 90 gal tank I would turn it on end, top out, and build a dart frog terrerium. Again thats me.
Best of Luck

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Jeremy
"I am become death, the destroyer of worlds" July 16, 1945 Robert Oppenheimer
1.1 Double Het "Sharp" Snow RTB's
1.1 Hypomelenistic RTB's
0.0.16 Hypomelenistic RTB's
0.2 Pastel Hypo RTB's
1.0 Double Het Stripe Albino RTB's
0.1 Suriname RTB
0.0.15 Normal Suriname Hybrid's
0.1 Anerthrystic RTB
3.6.17 Red Bearded Dragons
1.1 Rhinoceros Iguana's
1.0 Green Iguana
1.0 Ball Python
1.1 Cream Golden Retrieviers
1.0 Pomeriaian
0.3 Catus Terribilis
0.1 Spouse
1.0 Child