I rode a 2003 Hardrock exclusively for 7 years and I still have it (though it is disassembled at the moment). I added a Jandd Expedition rack that I got for a good price and have been more than happy with it (I still use the rack daily on my current primary steed). The nice thing about the Jandd is that if you have big feet it gives you a few more inches to slide back panniers for heel clearance on bikes with short chain stays (like most MTBs). My wife has a Hardrock of a much smaller frame size and it also fit a Performance brand rack without problems (I just had to bend the rack stays down a bit, but easy install).

Here is my 2003 Specialized Hardrock when it was mostly stock, but with Crank Bros Mallet pedals, Jandd expedition rack, and Michelin 26x1.5 semi-slicks. I later added Planet Bike Cascadia fenders, which I really like: