Tripsta is an easy-to-use flight comparison app with an attractive user interface.

You can sort by price, departure time or return time, and filter by max stops, flight duration and total price. A quick comparison with Skyscanner shows that the flights Tripsta found are on par.

One advantage is it lets you book in the app (unfortunately for a large fee), but it doesn't give you any flexibility on dates or join up with a hotel service to offer you the complete package yet.