I have noticed that with all online travel sites, you have to leave and return on the same airline (or partner) for international trips. Is there a way around this? It seems as though when you try to book a one-way flight it always ends up the same price as a return.
It depends - for example, in South America - a return flight is almost always cheaper than a oneway flight. I have no idea why, but seriously, this often works out.
What I do is load up kayak.co.uk or similar flight search engine. I do 3 searches:
This way, if two individual airlines are cheaper than sticking with one, then you'll find it. Ie if 2+3 < 1, you win! And if not, then you rest easy that you've gotten a great rate.
If you're really fussy, as I was a few years ago, you can search intermediate locations. I found four separate airlines that got me to Cairo and back on 4 flights, which worked out cheaper than a direct :)
(London to Brussels to Cairo, to Cologne to London)
This depends on airline policy - because they don't want to send airplane from A to B full of people and return it empty - this causes that two one way tickets are more expensive than one two way ticket with one company ( they have insurance that you will fly both ways )