... DSO's
oooh yes the faint fuzzys elusive little buggers they are! i think the best investment to see these is ....DARK SKY though like its already been said... bigger your light bucket the better. remember this the power of squares and telescope mirrors.! 2"^2 = 4, 3"^2 = 9, 4"^16 5"^2=25 once your hitting 8 and 10" that ^2 becomes noticable!
but the best thing to do is go to your local astro club and have a look though some of their gear, talk to the people touch some of the stuff. theres no use getting something only to sell it a few months on for something that will work for what you want