Two pages and no one's mentioned a Front Intake? If your case has a space for it, a lower front intake will be a huge benefit. Cool air in the lower front --> warm air out the upper rear. I agree with the idea to grab another exhaust fan for the space above your rear one now. Get a can of canned air and blast all the dust (if any) from your heatsink. Try separating your HDD's by a slot or two to allow them to cool better (the pic looks like they're right on top of each other?).
Edit: Also, get a second opinion temp-wise from another monitoring program. Some of them don't always play nice and give skewed readings.
Edit: Also, get a second opinion temp-wise from another monitoring program. Some of them don't always play nice and give skewed readings.