okay... here we go.
i would say no to pretty much any shark... not only do most of them get too large for a ten, they are pretty agressive, much more so than a dwarf gourami would be.
i wouldn't try any other gouramis either, as they will get cranky and territorial with each other, especially if you end up with more than one male.
male bettas, as you already learned... no way. a female betta, however, would be just fine in my experience. i've kept them with a blue, neon dwarf, and honey gourami in three different tanks.
barbs: if you were setting up a 29, i would say go for it. however, they prefer to be in schools, and most of them get too big to keep a school in a 10g.
cherry barbs, however, are the odd ones out. they stay smaller than most of their relatives and don't really school... they're kind of lone rebel fish, so you could have one or two of them in your ten, no problem.
i also have two gold barbs in a twenty long.. they are great fish to have... but IMO they are a bit large for a ten.
loaches: great fish to have, not so great in a 10g. just like the barbs, they should be in schools, and get too big to school in a ten. the kuhlis are kind of an exception... they are like a one inch fish that has been flattened out an extra two inches
other species to consider:
danios
white cloud minnows
tetras
corys
otos
rasboras
EDIT: caps beat me to most of what i was going to say... but yeah..
