The FDA recommends no more than 2500mg of sodium per day. This includes sodium from all sources (sports drinks, snacks, etc.). I've seen single meals that had this much sodium in them. So in reality, almost all backpackers could benefit by reducing their sodium intake. On hot days, you might need more sodium to manage your hydration (or simply do as I do and drink more water).
I don't have any unique recipes that are low sodium, but as Sabar has suggested, for several years I've substituted low sodium alternatives into my meals. Some products that are available in low sodium versions include:
Bouillion (both chicken and beef)
Oatmeal (use "quick" instead of "instant"
Canned tuna and chicken (I unfortunately haven't found low sodium versions in foil packs yet)
Curry powder (available at Wild Oats and other health food superstores)
My favorite zesty spice is Chef Paul's Pizza & Pasta Magic which is great on most dishes and adds no sodium.
I also simply eliminate adding any salt to recipes and I haven't been able to tell the difference in taste.