120mm coolers don't fit in the cosmos s without some cutting away from the side fan's surrounding trim. Actually my (Newegg.com - XIGMATEK HDT-S1283 120mm Rifle CPU Cooler - CPU Fans & Heatsinks
) fit horizontal, but to mount it vertically, blowing out he back of the case, I had to cut away from the side fan case.
-Right know I have my q9550 overclocked to 3.8GHZ with that cooler in the same case. Idle temps 42 39 41 38.
-Also recommend purchasing case fans.The case comes with 4 fans (3x120mm and a 240mm, while there is spots for 7 fans (6x120mm and a 240mm) I recommend upgrading the stock fans too, they don't seem to move much air.
I have 3 thermaltake red led fans accross the top. The stock red led in the front on the HD cage. I recently just customly mounted a fan above that one giving me 2 fans in the front. Dropped my case temp almost 5C. I also want to upgrade the my remaining fans to some scythe (Newegg.com - Scythe DFS123812-3000 "ULTRA KAZE" 120 x 38 mm Case Fan - Case Fans
) suspose to move a lot of air.
-also if you plan on getting a tower cooler I recommend getting one of these
Newegg.com - XIGMATEK ACK-I7751 Retention Bracket - CPU Fans & Heatsinks
I don't know what your future plans are, but I would recommed at modular power supply. I heard good things about this power supply.
Newegg.com - CORSAIR CMPSU-620HX 620W ATX12V v2.2 and EPS12V 2.91 SLI Certified CrossFire Ready 80 PLUS Certified Modular Active PFC Power Supply - Power Supplies
-Finally I love the case. But beware it is huge! I feel like I could have gotten a mid size case, but if you like me and plan on water cooling in the future then the bigger size case is nice.
Look thats a 4870x2 in the case. Lots of room, but make sure you have space for such a big case. Enjoy.