my last few forts have been in challenging environments. places like deserts with no trees or flux or iron.
ive turned huge profits to get the steel i need through getting retarded amounts of cloth from the elves and leather from the humans, and then trading masterwork dyed clothing covered in goblin bone spikes to the dwarves for full sets of high quality steel armor and weapons. in treeless environments elves also bring much needed wood. sometimes, especially early on, they bring crazy useless stuff, but in successive years they seem to catch on that what i buy i want more of.
also, trading with humans who live on a coast/river is great. so much turtle shell its not funny, and every dwarf in my fortress is wearing carp or shark leather. if you request it from the merchant humans can also bring a lot of dye.
im normally not that interested in the tame animals elves bring, i much prefer wild ones (the tame ones wont fighty with my dwarves in the combat pit) but i have got breeding sets of wolves, dire wolves, grizzly bears and the like.
also @ stormrage, im very sure you cant breed giant cave spiders, unfortunately. even if you get a tame male/female pair they dont have children. i think i recall some old attempts at modding this in resulted in the sudden appearance of 6 fully grown wild bloodthirsty GCS appearing when the mother gave birth in the crowded dining room. you can use modding in conjunction with utilities to get them though. personally, i find smelting things like GCS easier then attempting to get them breeding though.