Expand the range of speakers. Make a 2.0 desktop speaker setup with excellent fidelity and power. The SP2500 is great but in short supply and too bass focused. Ditch the external remote and subwoofer in favour of quality.
Motherboards. I mean, Corsair already makes RAM, SSDs, PSUs, various coolers and input devices. What better way to tie them all together than with Corsair motherboards? Especially if they bring that Corsair aesthetic to bear, I'd be down.
If I could pick any product to make, it would definitely be a robust & universally compatible GPU replacement heatsink/fan assembly...something comparable to what Prolimatech and Thermalright have put on the market! At the right price point it would be a great product.
There are honestly a lot of products I'd love to see Corsair make since so far every Corsair product I've owned has impressed me with performance and quality. I think I'd like to see monitors or speakers though. Somehow I could see them outperforming everything else.
A mini-itx case that is small enough that it could be mounted to the VESA mounts on a monitor. Though there would have to be trade-offs going so small, I figure Corsair could extract the most out of such a small sized unit.
Pre-fabricated water cooling kits that are modular and work with Corsair components designed for both air and water.
Sell the base CPU only closed loop coolers but have a higher end modular kit that will then work with air/water cooled Corsair RAMM. The kit can also be used in collaboration with other graphics and motherboard manufacturers designs much like modular water block hold down kits.
Monitors seem like the next logical product to tackle. However, what about software? Seems like the corsair link is a bit half- baked. I would love some better monitoring of low level components and voltages etc. The asus mobo tools always seem to lag and crash.