Garnfellow said:
There is no publisher that can even come close to touching WotC for production values. None. Period. Seriously, is this a loaded question?
How do you define 'production values,' anyway? Color art? High-quality paper? The inevitable search for ever more cumbersome and infuriating hardcovers

?
Sovreign Press uses all color art and
glossy paper for their entire Dragonlance line. Glossy!

I'd probably have to give them the nod as having the best production values overall, unless someone knows of a critical flaw in their books - a recurring binding error or some such. Of course, they're sort of a second party publisher with direct ties to Wizards.
Sword & Sorcery Studios' Warcraft books, except for the computer graphics in the current one, have better-than-WotC production values, especially when you consider that their art is electronic game concept art quality - a tier above, at least in terms of pay, I wager.
AEG's Spycraft (I know, non-D&D, but this isn't a direct response to the OP) was all color art, nice paper, in a stupidly thick, heavy-bound hardcover. What hardcovers they have produced for D&D, like the original d20 Rokugan book, have been of WotC caliber.
Mongoose's entire Conan line is full color. Initially, I would have said the art was at or above WotC level, particularly the gorgeous covers, but it seems they're reusing cover images now. :\ I seem to recall some binding issues with the core book, too.
Only Sovreign Press has met WotC production values consistently.
Of course, given the choice between two black and white softcovers for $19.99 each and one color hardcover for 34.99, I'll spend $5.00 more to get the softcovers; the weight and convenience is easily worth extra cash and the loss of color art.