Honestly, the biggest fault of Google Maps is that I can't find something "along the way" to something, just nearby. I'd be much happier if I could specify "TGIF's on the way to Alice's house" or "Gas stations along the way to Las Vegas near the halfway point."
I can't get too mad at it, since I can just zoom out and it'll search from the center of the map - but it's not very effective if the distances are long or if I'm using the text interface.
TomTom will actually do this. You can specify that you want to go to a gas station along your route and it will list all of them and the detour distance required. Unfortunately TomTom makes you pay for live traffic data.
You can add extra location to directions by clicking the + to the bottom left of the existing ones (in browser at least). Although I'm not sure if that works with generic locations (like gas stations etc)
I can't get too mad at it, since I can just zoom out and it'll search from the center of the map - but it's not very effective if the distances are long or if I'm using the text interface.