Chitchat,
I've done them. Though "done" might be an exaggeration; a group of us flew to Paris, and we flew through them to the Paris Heliport, and out by the same route.
They're not complicated; they follow the Seine for a lot of the route, much like following the Thames in London. You're at 1500 ft though, and can't descend until very close to the heliport, which makes landing interesting.
The thing I remember most is how nice ATC were when we got lost. My co-pilot and I were relatively low hours PPLs at the time, who'd never flown in France, so the CFI put the whole route on to the GPS for us, including the entry to the heli-routes. Or that's what he said he'd done anyway. We were approaching Paris, when we realised we didn't have the entry for the heli-routes on the GPS. I was navigating, and assured Ian I had it, it was that gap in the woods, then that loop in the Seine. Well, one gap in the woods and one loop in the river looks much like another, and it was when we realised we were approaching the Arc de Triomphe and not where we should be that I made one of my more memorable radio calls:
"Molyneau...er..I'm sorry but we're not where I just told you we were. In fact...I have no idea at all where we are".
They calmly gave us a squawk, identified us, and directed us back to the heli-lanes. I really can't see Heathrow being that laid back about it if you did the same thing in London.
Sorry, don't know about any on-line guide.