I started out with an inexpensive Blackburn rack on my 2005 Sirrus commuter. When I decided to try a tour on the same bike and started investigating panniers, I was pretty surprised by the total weight of most popular rack+panniers combinations. I know a few ounces here and there isn't a big deal for touring, but go look at the weight of one of those Jandd racks and Ortlieb panniers--not exactly negligible. So I went the opposite direction: Tubus Fly and Lone Peak "King's Peak" panniers. This saved me something like a kilogram, I have no heel-strike issues with US shoe size 12 1/2 (on a Sirrus no less!), and the rack is rated to 18 kg. If I need to carry more than that, I'll want the extra weight on the front wheel anyway.

This combo worked just fine for a four-day trip on the Olympic Discovery Trail, including a couple nights of camping. Clearly, if you're looking at a trans-america ride, or bike trekking in Mongolia or something, your requirements may differ. But I've been very pleased so far that I started out simple.