Introduced in March last year, this is a fantastic free online resource provided on the Bristol City Council website, with funding by the English Heritage.
The Know Your Place site starts with a Modern Ordnance Survey map which is searchable. This can then be overlaid with various historic maps of the city, my particular favourites being the Ashmead maps of 1854.
 
The one gripe I have is that the searchable index only covers current road and streets. This can make it extremely hard to locate those streets which have been renamed or no longer exist. The only way I have found to get round this is to locate streets in close proximity to the one you are looking for, such as the listing out the next streets on in a census, keep looking until you find one of these on the modern map and then go to one of the maps showing that area closest to the year of the event, and fingers crossed you should find the street you’re looking for, it may even have some house numbers shown.

This website gives you an opportunity to locate the streets and sometimes the houses where your ancestors lived. I cannot recommend this site enough, I only wish it covered a greater area.

http://www.bristol.gov.uk/page/know-your-place