Just a quick note here - a CPU heatsink is required - period. If you aren't overclocking, the original retail heatsink will be sufficient. If you are overclocking, then a higher-performing aftermarket heatsink would be the way to go.
Yes, if you plan on overclocking you'll require a CPU heatsink. Though, if you only intend on running your hardware at stock settings, it won't be necessary.
Just to avoid any potential confusion.