Depending on the species of clown there are any number possible tankmates in the 29. Examples: various blennies, gobies, dragonets, pygmy angels, certain damsel species, and so forth and so forth. . .plus a wide array of inverts as well.
As usual . . . .it's really more of a case of what would you not want to keep with them
agreed, and don't forget, firefish, hawkfish, mid-swimming blennys and gobies, cardinals, jawfish, fairy wrasses, and pretty much any "nano fish" that you can find