Just a side note, but sand sifting gobies do not "help" with the sand bed. They eat the micro fauna in the sand bed that eats waste. If you want "help" with the sand bed nasserius snails will help turn in the waste so it can be processed but only eat larger meatier food and there are also tiger-tail cucumbers that will turn the sand and eat detritus out of it but leave the micro fauna alone.
Otherwise, if your just wanting a cool looking little fish Ramsey's advice is right on...
88g L shaped reef
150g freshwater cichlid