Ace (
www.wowace.com) offers a fairly snazzy minimap-based mod called AuraMap.
this will paint circles on your minimap for yourself and all your party members, showing aura ranges, healing ranges, and etc. i have been playing with it. so far, it is looking pretty effective.
many "healing" mods (grid, healbot, others) will also range check, and change the alpha on a party/raid-member's element on their display when they go out of range. digging into their options might get you want you want.
hope this helps.