17 gallons is too small for goldfish...they're social fish, and i can't see having more than a single goldy in there unless they're newborns due to their massive waste output. if i had a spare 17g, i'd put some imbellises in there, but that's only really an option if you're able to grow and cultivate a lot of live plants for cover. a guppy tank would be wonderful though, especially if it's a tall tank (guppies like a lot of up-down swimming room) if you go that route, though, make sure to use very soft decorations though, the longer-tailed varieties have fins even more delicate than a betta's.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)