Pereskia aculeata is supposed to have good fruit, and has been named the 'Barbados Gooseberry'.
Rhipsalis fruit is also edible.. the ones i tasted were very bland though.

Dragon fruit [Hylocereus undatus]. I have one small piece but it is readily available here. A chap comes into the markets on Thursdays and will being me any amount if I let him know the day before.

SELENICEREUS MEGALANTHUS!!!

Pitahaya/yellow pitaya
sometimes called 'yellow dragonfruit'

omg.. by far and large the best fruit you will ever taste from a cactus. far superior to hylocereus undatus IMO.

also this produces the largest flowers of all cacti!

Found this mob on the web, dunno if they are still trading but their page looks interesting none the less.

http://desert-feast.com/cact_n_z/sc_stell.html

Nice link, shortly. It's quite good to be able to browse through that list of plants.

Lewis, have you found anyone who sells S. megalanthus plants? It's one species that I'd really love to try growing.

i have this one - i recently propagated it from seeds. i could try and get you a fruit or a cut (lady at markets sells them) or could send you one of mine when they are a bit bigger
edit: yellow pitaya is what im talkin about

Cheers for the offer mate, but another member here has already helped me out.

I'm really excited about growing this plant, although I suspect Melbourne weather may impede growth and flowering somewhat.

oh goodo. you've got yourself a challenge there! they are really nice fruit, like a kiwi thats not at all sour with a softer texture. mmmm

Well, I'm moving into a new place soon, and one little project I have in mind is setting up a small greenhouse in which to grow fruit-bearing cacti. I've got indian fig, both the red and pearl dragonfruit and now yellow dragonfruit, so come summer time I should be able to get a reasonable crop.

A fresh, chilled dragonfruit for breakfast has to be one of the best and most refreshing ways to start the day...