(2-part post):
Hi VHG,
I'm not really the best person to ask about accommodation because many of my foreign excursions are day trips! (I live less than an hour from Stansted, so I watch out for Ryanair bargains to Dublin, Genoa, Barcelona, Valencia, Rome, etc. I usually have about 10 to 12 hours to explore but I do plenty of research in advance, so I still get to see quite a lot. I rarely book accommodation).
However, there's certainly one website which is the first place I look when I'm trying to suggest budget accommodation for people. It's HostelWorld.com. Don't be put off by the word 'hostel' in the name. If you use the 'Additional Search Options' you can select 'Guesthouses' and 'Budget Hotels'. If enough people have stayed at a particular hotel, in the last 6 months, to provide a meaningful average, you'll see a percentage satisfaction score alongside each hotel. Even if no score is shown (because not enough people have submitted reports) there are often a few reviews available if you go to the hotel details and click the 'Reviews' tab:
http://www.hostelworld.com/
If you're flying with a budget airline, it's worth looking for an 'Hotels' link on their website. Ryanair link to HostelWorld (that's how I discovered it) and also here:
http://tinyurl.com/3bbdyc
easyJet's hotel site is here:
http://tinyurl.com/2hg3zr
(It's actually fed by Hotelopia)
You don't have to book flights with an airline to use their hotel booking service