i use
www.skyscanner.net it gives you a list of a bunch of airlines and then sorts by price. it is applicable to pretty much any airport so it is nice in that regard. i suppose the only problem with it is prices are listed in GBP, but its not really a problem because for buying you are directed to the airlines site.
check aircanada.com as well. Two weeks ago I booked 2 flights to London in July for 800 bucks each (taxes in) which is ridiculously cheap for that time of year, I would imagine flying in April would be cheaper.
As for the new question... try
www.tripadvisor.com I find the reviews are extremely helpful on that sight.