i have really curly hair and if i've taken the time to flat iron, i want it to last as long as humanly possible. i also have a bad habit of ODing on shine serum and need to mop up my head without taking a shower... :shame:
i've used the bumble and bumble powder, dry shampoo (it's aresol and usually avaliable in hospitals), babypowder and shalimar body powder. i like the perfumed body powder best (i'm a freak about matching scents) but since they discontinued the one in the bottle and now only have the puff i conserve what i have left....i use baby powder most of the time. babypowder is the most finely textured, CHEAPEST, most avaliable and smells better than the others. the only downside is it's hard to blend for brunnettes. you have to work it through your scalp with your fingers REALLY REALLY well, and even then sometimes it still shows.
brushing helps, but sometimes that can make your hair look flat/greasish again if you end up brushing the powder out before it can absorb anything...not a good look.
it's also really important that you use name brand baby powder...i know right? why quibble about 2 dollars...but you'd be suprised how many people do. i like johnson and johnson best. the store brand is super clumpy and will not disperse well even on blondes.
i wasn't crazy about the bumble and bumble...it didn't do any better job absorbing oil than the baby powder and it smelled funky (hard to discribe but kind of powdery/medicinal and plain weird) it was MUCH less hassle to blend than light colored powder but to me (even as a chestnut brunette at the time) it wasn't worth paying 10x the price and searching all over for a bumble and bumble salon in my podunk state. once i found some though, the little bottle did last almost a year, which was nice...but my HUGE 3 dollar bottle of baby powder lasts that long too. hehe. the bumble and bumble does what it says it will...since you're a dark brunette the easier blending might be worth it to you. it comes in four different colors (blonde, red, brown and black) and all the colors are on the way warm/red side except the black which looked pretty neutral.
i have dry skin and hair and have gone up to 10 days between restyles/shampoos using powder to absorb oil...but my sister is oilier and can only go three or four.
hope that helps!
OH and you can also use aresol hairspray to absorb oil and silicone hair products if you've overdone it and you're in a pinch. i like sebastian shaper and shaper zero.