i got a cooler master 1000 for my build a few weeks ago, and it has been really good to me.
if you plan to overclock your system (and i mean really overclock, i have my CPU, RAM and SLi graphics cards all overclocked), i would recommend a few case mods:
1: if you r only using 2 of your front drive bays (which is the norm for most ppl) use the bottom 3 to install a new intake fan
2: install a fan either above or below your hard drives (only really necessary if you have multi hard drives) (also, take out any empty hdd trays, it will help airflow)
3: make sure your CPU fan is correctly orientated. this basically means, hav the fan facing the direction of the cold air (in the cm cosmos case, this is facing the bottom of the case), this may sound simple, but in a full tower case like the cosmos, it can really make a difference.
you mite also consider changing the stock 120mm fans to 140mm fans, but i have and i cant really c this doing much of a difference, considering that if u do all the other things, your case is going to feel like an air conditioner
EDIT: i 4got to include this:
there is a clip on youtube that gave me these ideas to make the mods to my case, can't remember the url, so just search coolermaster cosmos case mod and it should be pretty easy to find