score:2
I use momondo.com. They aggregate results from other travel agencies and they offer a nice map search feature. Find your city on the map, find the conference venue and then look for hotels nearby.
Upvote:1
I use booking.com. What I really like is that you can cancel any booking up to 24 hours before arriving.
Another way is to use google maps. First locate the venue, select the appropriate scale and then type hotel in search field. The surrounding hotels will popup around your conference venue.