Thanks for the input.
We don't have a Costco in New Orleans (yet, they're finally building one here, 1st in LA, but not ready to open yet)...so, that's not an option for now.
What size images do ya'll upload for just regular prints (4x6)? What size jpg or tiff?
Do these places usually by default try to do color correction? I"ve already done all the post processing I want on my images, I don't want any other processing on color....
Again, Costco will ship prints just like any other online printing service, so I wouldn't necessarily rule them out.
Costco supports .jpg, .gif, .tif, .bmp, and .png files.
As far as image size is concerned, I'd upload the full-res versions even if you're just going to print 4x6's since you might, at some point, want to print larger sizes of your images. The only drawback is the time required to complete the upload.
Costco has an option to turn off auto color correction when ordering your prints, which is what I do since, like you, I've already done them in post.