Lodging

Short Term Lodging Options

Hostels, hotels, and home stays are the options in this category, apart from crashing on the couch of a stranger in a foreign country; the latter option is not typically recommended.

Backpack Europe - Information on and bookings for hotels, hostels, camping, and other opportunities.
Hostel Bookers - No booking fees for hostels.
Hostels.com - Prices are similar or less than walking in. Provides reviews by previous guests.
Hostel World - Hostel bookings and links to city guides, pubs, clubs, podcasts.
Bed and Breakfasts UK - U.K. bed and breakfasts and travel guides.
STA Travel
AllStays.com - Information on and bookings for hostels and other lodging.

Longer Term Lodging Options

Short term apartment rental for stays of one month or more in duration.

Investigate regional physical and online bulletin boards. Craigslist has some international listings. Check any local universities for online postings as well as local newspapers and other community sites.
Universities may allow you to rent their excess housing to you for longer durations.
International Home Exchange Network - Listings and arrangements for exchanging lodging with other individuals. Also has rental listings.