*guppies (common, or even fancy for MOST room temp, if you don't believe in heating your house during the winter, then no)
*danios
*rosy red minnows
*white cloud mountain minnow
these are all small and would fit in a 10g (not all together of course). but I wouldn't recommend them with goldfish as goldfish get big and tend to put everything in their mouths, including smaller fish.
Dojo Loaches, also called weather loaches. They are an eel looking fish that can grow over eight inches. They come in the standard gray and also a "golden" albino variety. You may also find some with minimal patterns to them. the above answerer listed a few different types of goldfish. Keep in ming that you will need about 20 gallons per goldfish so if you don't have a nice sized tank I wouldn't add any more. Goldfish are very dirty and get very big. Over time they will put off more waste than a small tank can handle and you will have numerous water quaity issues. always go for bigger tanks with goldfish.
and no koi. koi get over two feet long and require at least 50 gallons per fish. while they do get along fine with goldfish, they are schooling and should be in groups, so unless you have about a 300 gallon tank I would skip these pond fish. ALL goldfish get at least a foot long if the comet or shubunkin variety or the size of a softball if the 'fancy' variety. All koi get huge.
American flag fish,All danios,gold barbs,cherry barbs, ruby barbs, koi, plecos in the summer. People will tell you bettas DO NOT LISTEN, bettas need a heated and filtered tank because they come from warm china rice patties.
white cloud mountain minnows 15-23c
danios 17-26c
and
leopard fish
http://petmart.co.nz/cart_product6916-1-.html?Search=leopard&Start=1&Title=LEOPARD%20FISH%206CM