when i got my 690 my step dad had 2 low speed nexus fans lying around. i tossed both of them into the top right above where the CPU is. i left the stock fans venting out the back and on the side, and pulling air in in front. i put a 140mm low speed yate loon that i ordered from frozencpu in the bottom. case has space for one more on the side door but my Vendetta2 sort of gets in the way. case hardly whispers with all those fans with the door on and i can literally feel the airflow around it. alternatively, you can just replace all the fans in the case with low speed nexus fans or yate loons. it has so much space for fans that getting highspeed fans just doesnt really make much sense. the airflow with my configuration is incredible though. the Athlon 64 4000+ in that rig runs at only 25c at load lapped, with a lapped vendetta 2. cpu isnt overclocked, but i undervolted the hell out of it. it ran at about 32c load in my old case.
ed: i forgot the top can take 140s natively. i used 120s since i already had them, but what aigo said is probably a really good idea. the 690 is one of the better cases i have worked with in the mid tower size range. i will probably get another at some point and compare having a ton of 140s vs my current configuration
as for the quality of yate loon fans vs nexus fans, i think both are great. i have a whole ton of yate loons in my current case, and i can really tell the difference between the ones that are and the ones that arent. all the yate loons are running in the stock fan brackets for my case (Thermaltake Armor), which arent very great, and running virtually silent (you cant hear them over my nb/sb fans). in comparison, the 92mm AC Ryan fans i got (i wanted the colorful pretty fans) actually vibrate in the brackets when i turn them down to lower speeds on my fan controller, and i will be replacing the brackets with rubber fan grommets as soon as my last order from frozenCPU comes in.