In the evening on Pub Street you will find various street food and alcohol vendors (tuk tuks with bars attached), countless patios, and several clubs (Temple Bar and Angkor What? are the main two across the street from each other) blasting music at insanely loud volumes in hopes that you will come and drink buckets at their location, which eventually turns into a street dance off party where you'll usually find a local Khmer girl (who sells bracelets) out-dancing everyone who challenges her. She may even challange you to a game of rock, paper, scissors as well. And while I did have a great time on Pub Street the first evening I arrived, I found it to be quite old and repetitive very quickly on the subsequent nights as you will hear the exact same tunes each night. Other unique bars to visit not located in Pub Street include the Mad Monkey Top Banana rooftop bar located at the top (obviously) of the Mad Monkey hostel, the entire bar is beach sand which is pretty awesome to play some beer pong in. The other bar I enjoyed was X-Bar located not far from Pub Street. It is a multi-level facility which features beer pong, pool tables, live music as well as a rooftop half-pipe which the legendary skater Tony Hawk even skated at one point last year!
The temple tours were the real reason I came to Siem Reap though. I ended up completing two different temple circuits which I was easily able to book my tuk-tuk ride with through my hostel, though you can likely ask any driver you see and they can do the same. The first day of my tour called the Small Circuit included stops at Angkor Wat, Bayon, Takeo, and Ta Prohm. The second days tour I completed called the Grand Circuit included visits to Preah Khan, Neak Pean, Tasom, and Pre Rup ... I may have misspelled a few of those. Each days tour took about 6-7 hours, and even then we only ended up seeing a small handful of the extensive network of temples in the area as you can see from this thorough online Temple Guide. I would highly recommend using the tuk tuk drivers to visit these temples as you will do quite a lot of walking throughout the day in a very hit climate and will be very exhausted by the days end.
Siem Reap is a great city to visit if you planning to come to Cambodia. I'd recommend renting a scooter or pedal bike as well to get around the place so you can adventure a bit further outside the core of the city.