Catfish that have small mouths would suit the tank like cory cats. They like to be in groups of at least three. Best to stick with a group of the same species rather than mixed. Looks more balanced that way too, IMO. Kind of neat to see a school of the same little guys swimming together.
Unfortunately, not much for choice in compatable whiskery catfish for the fish you have. Corys do have some whiskers, but not like silver tip sharks and pictus cats, both which are not suitable for a 30 nor for the fish you have. Most have big mouths and whatever can fit, will eventually go in...even if it takes the thing a few years to dine on his roommate...lol...gotta love fish...
Rainbow sharks and other similar loaches get too big for a 30 gallon. Best to avoid.
Some nice "show" fish or centerpiece fish:
*A male dwarf gourami would make an excellent choice. Varying colors to choose from too.
*A single angelfish would be nice and compatable (single rather than paired to avoid spawns that can create mass hysteria to the other fish...angels will thin the population to protect their eggs and fry).
*Neon blue rainbowfish are beautiful and would make a very nice addition to any friendly tank. Males and females can be sexed easily (red fins = male/yellow fins = female). Adult size is just 4".
*golden wonder killifish are another top dwelling species and the males are vividly colorful. Absolutely gorgeous.
*Rams!!...yes rams
Blue rams, yellow rams, longfin blue and yellow rams and balloon rams also long fin balloon rams...lol...great fish. Very pretty. I highly recommend german blues...the males are stunning. Do make sure water quality is pristine for these fish. Hardy so long as their water specifications are met, which is fairly easy to maintain. You have driftwood, so half the help is already there to help maintain a nice soft to neutral pH and a few plants would make them very happy.
Do keep in mind that you have plenty of middle swimming fish. The cory cats would nicely fill in the bottom portion. A small species of pleco like a little bushy nose or rubber lip would do fine too (and nice for peaceful algae control). The gouramis would fill in the top portion of the tank. Rams defend territory toward the bottom, but encounters are rarely fatal. They do a lot of chasing from their very immediate surroundings and is the bulk of their bite.
Do note: Bolivian rams are one of the hardier species of rams, but because they are bigger than the others, a single adult would be best rather than paired.
Selecting species that occupy different areas of the tank can help you maximize population capacity...but make sure there is enough porous media and good water flow to keep nitrifying bacteria in top shape for the waste load and avoid over feeding.
The tank's water volume will limit your choices and population capacity. You are almost at full capacity...largely due to the buenos aires tetras. They are a larger sized tetra...I have seen four inchers...but I think that may be the max.
Always read about the fish you are interested in before purchasing and make decisions based on the capacity of the tank rather than your love for fish. Otherwise you just may need to get yet another tank
HTH