If you're after ultimate image quality and detail under controlled (studio) settings, then the "usual suspects" are not what you're after. There is a reason why commercial shooters use medium format cameras, and it's not just about the megapixel count. Of course, a Hasselblad H4D/H5D or a Phase One IQ back is going to put your "pricey combo" remark into a whole new context, but that's not the only solution out there.
On a per-pixel basis, the best out there at the moment is arguably the Sigma SD1 Merrill with any of Sigma's very nice macro lenses. Honestly, the camera is the next best thing to useless at ISOs above 400 (and is best kept to its lowest ISO), it has lousy general-purpose handling, and is missing a lot of de rigeur features when compared to just about any other current DSLR out there. Oh, and you have a limited number of lenses to choose from, have to special-order just about everything, and are stuck with Sigma's RAW processing software for conversion (to 16-bit TIFF so you can finish the job in something that's actually worth using). But, my goodness!!! the image quality. Between the Foveon sensor (which means that each pixel completely determines its own colour values) and the lack of an AA filter, the amount of colour purity and per-pixel detail is something no Bayer-filtered sensor can even approach.
Again, the SD1 Merrill is only really useful under controlled conditions and would be a disappointment for general photography. And at about $2000-2300, it's arguably more expensive than it ought to be, considering its paucity of features and APS-C-sized sensor (but not nearly as much so now as it was at the original $10,000 price tag). But if you want top-notch product/pack shots under studio conditions, you really can't get better until you step up to medium format.
(If you want to see what the sensor can do, check out the review of the fixed-lens DP2 Merrill at the Luminous Landscape. The SD1M, proper, is reviewed at Digital Photography Review, and the original SD1 is reviewed at Luminous Landscape (there's a link on the DP2M review page), complete with legitimate comlaints about the original price and missing features. Sigma's macro lenses, in various non-Sigma mounts, are reviewed well at Photozone.de; you should compare across brands to see what the intrinsic quality of the lenses are when the mount-specific characteristics are eliminated.)
