Biggest fish I have kept personally.. well... i had numerous fish that all got to a foot long, 30cm and maybe up to 40cm for some... before i had to stop keeping fish and sell up.
Kept:
Pearl Arrowana who got to 35cm...
Silver Arrowana who was 30cm...
Sorobim Limia Catfish was easily 30-35cm...
Tyre Track Eel was 30cm and my ex has him, he is more like 40cm now.

my beloved Mr Eeler.
Fire Eel got to about 40cm... impressive for a non feeder
Vieja Synspillum (not vieja any more, cant keep up with the names!) got to 25cm
Oscars.. we had about 4 that were all about 30cm...
Tilapia mariae... about 25cm
Potomotrygon Sp stingray... Raymond was about 30-35cm accross his disk with another 20-25cm for his tail!! He was big!
Had lots of big discus and angels and other catfish but they were the biggest.
At work.. biggest i have delt with was probably 60-80cm catfish like Boris the Giraffe Catfish, Buster the Perruno Catfish, Buster the Mystus Wykii Catfish, Red Tail Catfish, Silver Arrowanas, 60+cm Fire Eels, Pangasius etc...
Not to mention the big variety of foot long cichlids like oscars, jaguars, nandopsis istlanum (though name changed again i think), geophagus, goldfish, the bigger koi and sturgeon and sterlets etc...
I love big fish! But they just HAVE to be kept appropriately. I had a nice 8 x 3 x 2 tank and sump that was about 1700L all in and not to mention a lot of other good sized tanks and indoor ponds.