first, as a basic rule of thumb with buying pants, i tend to only buy brands that are labeled by waist size and not the normal 0,2,6,8+ sizes as they usually tend to be smaller. coincidently, those are also the brands that tend to be more expensive, but a decent amount of searching at discount stores, thrift stores, and ebay will almost always result in a good find.
and onto the list:
diesel - sizes run fairly big, but some cuts are slimmer than others, but generally nothing over a 26 will fit any of us. a 25 tends to be a looser fit on me, so i reccomend a 23-24.
miss sixty - the ideal jean brand for the thin AND tall. these are always made very slim and very long. very true to labeled size, but might be too long for those of you who aren't very tall or have short legs.
earl jeans - also very thin-friendly. sometimes too thin-friendly even, a 26 is a little baggy, while a 24 can be too small. the cigarette cut pants are a godsend for the underweight.
helmut lang - sizes don't run very big, but are usually bigger than labeled.
seven - normal sizes.
paper cloth & denim - pretty small. but probably the most expensive on here.
marc by marc jacobs - usually pretty true to size-big.
levis - big and not very thin-friendly. smaller sizes are impossible to find usually, in my experience anyway.
we all know how gap, express, and old navy jeans fit, so don't bother with those.