I do all my regular 8x12 printing at Costco, because they quality is great and the price is right! On top of that, Costco has printer/paper ICC profiles available for nearly all of their in store photo labs. Proof your shots in Photoshop, convert them to the appropriate printer profile, and then take them to the store on a thumb drive. Go through the process as you normally would selecting your prints on the little kiosk. When you go to pay for your order, tell them you have color corrected your own photos and that (if applicable) they should be printed out on a particular machine. They'll do the rest! (Note: Some Costcos have more than one printer, and quite often only one has a profile available for it. Make sure they print on that machine!)
Given all the extra steps of using the correct printer profiles and a calibrated monitor, I've noticed that virtually all of my prints were a little dark. I was perplexed as to what could be responsible for this. Turns out, the genius of all things Photoshop, Scott Kelby, had this same problem. In his book, Photoshop CS3 Book for Digital Photographers
- Starting with the image you want to print in Photoshop, make sure the image is flat. That is to say, make sure it has only 1 layer.
- Press Control-J on the PC or Command-J on the Mac to duplicate the single layer.
- Change the blending mode for the new layer to screen.
- Then adjust the opacity of this layer to somewhere between 20% and 30%. Scott suggested 20%, I find 25% works well for me.