Tim Holtz inks RULE!
There are a lot of ink pad choices out there, but the best quality I have found thus far is from Tim Holtz Distress Ink Pads. They come in a wide variety of colors - anywhere from classic browns and black to mustard yellow - and last forever. Also, the pad and case itself are square, which, at least to me, makes them more easy to handle when you are using direct ink to paper inking techniques.
You are looking at my FAVORITE Tim Holtz ink - Walnut Stain. It is definitely a scrapbooking staple if you are in to the distressed look, but make sure you check out the other colors Tim has!
P.s. You should store these upside-down to keep the pad nice and wet. :)