Lillian Lake is nice. Although it's only about 4-6 hours (14km return) but the lake of the end is great. The campground there is closed due to flood damage so I don't know what the rest of the hike is like.
Picklejar Lakes is kind of a nice hike too, but short (8km return).
As far as knowing where to go, your best bet is to grab a guide book. A few I like
http://www.amazon.ca/Dont-Waste-Your.../dp/0968941974
http://www.amazon.ca/Scrambles-Canad.../dp/0921102674
http://www.amazon.ca/More-Scrambles-...T7BZ255BZKAP7S
Also trailpeak.com is good. You can select activity (hike/bike/ski etc) and the area you want to go to get ratings, reviews, routes, etc.
Hope that helps!