I love the NIK plug-ins, especially Color Efex Pro 3, Silver Efex Pro, Viveza 2, and HDR Efex Pro (just added to their product line). All of these are now 64-bit compatible and will work with A3 in 64-bit mode.
Their other plug-ins, Dfine 2 and Sharpener Pro 3, aren't 64-bit yet but should be coming along soon.
...I've been using the Topaz bundle demo through their Fusion application, and quite like it. I find I use primarily Adjust, but occasionally the Lens Effects. I'll probably buy Adjust. (no affiliation, just satisfied)
I tried the NIK bundle, but couldn't quite cotton up to it. Did the trick, but Topaz seemed more user-friendly for me.