Agoda – One of the best hotel finders, which consistently has the best deals!
Couchsurfing – Free accommodation, yes but thats not really what the site is about its a great way to meet locals and explore cities and areas that it would otherwise be very hard to access. Meet you host and they’ll normally take you to some local restaurant, or to a secret view spot, either way you almost always end up having a unique experience and making a good friend while your at it!
Air bnb – 9flats – Roomorama – People rent out their spare rooms or whole apartments for bargain prices! You can select based on area or price and its also a great way of hooking up with hosts that can give you advice on the area!
Tripping – Offers both free homestays and apartment or room rentals.
All these are a great way to meet locals, have a unique experience and see a different side of the area! And you can save money at the same time, most sites even let you pay quickly and easily with PayPal, so its completely hassle free even when your on the go!