The main reason most people come to Cambodia is to visit Angkor Wat. Siem Reap has been growing with the popularity of the temples. The town seems to polarise opinion. I thought it was way better than Sihanoukville despite some people telling me they hated it. I have absolutely no problem with a town that has a big tourist area where people get drunk constantly, as long as that's not the main reason to go! Siem Reap has Pub Street which caters to all the tourists who have had a long day at the temples and just want to drink until they can't see. I had one big night out there and really enjoyed it. Dancing on the street with about 50 people was the highlight. There's also a pretty great food scene in Siem Reap, so that kept me busy.
A single day pass for the temples is $20 and a 3-day pass (to be used over a 7-day period) is $40. So if you plan to do 2 days, you might as well get the 3-day pass. That's what I did and I had a day's break in between so I didn't get templed-out. It's worth noting that with the single day pass, you can actually use it from 5pm the evening before. So if you're really quick, you could see sunset twice!
As for tuk tuk prices to get to the temples, I think I paid $5.50 for roughly 3 hours at the end of the day to Ta Prohm, $9 for a set of 7 temples and $5 for sunrise to Angkor Wat. I think a full day is around $12-15. Prices might change with more than one person.
If you're interested in photographing the temples, there's very little point other than at the beginning and end of the day. The light is just so harsh that the photos will be pretty rubbish. However, during sunset you can get some absolutely amazing shots as the golden sun lights up the temples. This is especially true for Angkor War. I was amazed at just how empty even the popular Ta Prohm was soon after sunrise. Basically I recommend getting up early and doing a good few hours of the temples, then having a break until around sunset. The middle of the day is very hot, crowded and the light isn't good.
Accommodation
Millennium Guesthouse
Basic but good location and A/C for $13 (which is good for a private room during peak season in Cambodia).
Food
Genevieve's
The duck with tamarind was perfect! The lamb shank was tasty too.
Haven
Very popular social enterprise which didn't quite live up to expectations.
Dakshin's
Tasty Indian food and very nice owner.
Cuisine Wat Damnak
Very fancy and expensive tasting menu. Definitely go here if you're a couple and want a nice romantic dining experience.
The Touich Restaurant Bar
A bit out of town. I had the salt and sand snapper which was pretty good!
Nightlife
Pub Street
Loads of bars and restaurants. Fun if you want a big night out, but probably best to avoid otherwise.
Angkor What?
Good later on in the evening. People dance in the street.
Temple Bar
Opposite Angkor What?
Sights & Activities
Angkor Wat
Obviously. I did it both at sunset and sunrise. I much preferred sunset.
Ta Prohm temple
Overgrown with trees. Very cool! If you visit around sunrise, you pretty much get the place to yourself which adds to the atmosphere.
Bayon temple
Big faces!
Pre Rup temple
I did sunset at this temple on one of the days. Good choice!
Other temples
I visited all of the temples listed on this site (but in reverse order, finishing with Angkor Wat at sunset) in just one day.
Boat ride to Battambang
See in the Battambang section.
Food
Please use my Cambodia food guide which has all of my favourite places and dishes for the best food in Siem Reap.
Accommodation
Millennium Guesthouse
Basic but good location and A/C for $13 (which is good for a private room during peak season in Cambodia).
Nightlife, bars & cafés
Pub Street
Loads of bars and restaurants. Fun if you want a big night out, but probably best to avoid otherwise.