Siem Reap Transportation Choices

How to get around town...

Siem Reap is a small town. You can walk around the downtown area and still cover a lot of ground.
That said, there are several choices of transportation to get around this town. Especially useful when you're trying to visit the Angkor temples, whether near or far.

Bicycle
Since Siem Reap's terrain is pretty much flat, it's is easy to cruise around with bicycles. You can even go to Angkor Wat using bicycles, because although that's rather far, it is still doable. I personally think bicycle is the way to go for getting around town (once you get over the traffic quirks here).
You can rent a bike easily from your hotel or guesthouse. There are also many small mom and pop places that rent out bicycles. If you see several bicylces lined up by the street or major roads, you can be sure they are for rent.

The rate ranges from $1 - $2 per day, and choices vary, from a proper mountain bike with speeds, to the regular cruising bikes. They will also give you the bike lock when you rent, so you can wander around without worrying about the bike.
There is charity organization that rents out bicycles through guesthouses for $2/day. The proceed will be used to aid projects for the rural areas. You can find out more about The White Bicycles here.

Moto (Motorcycle)
Somehow, in Siem Reap foreigners aren't allowed to rent motorcycle and drive it themselves. So the next best choice is to rent one and hop on behind the driver. No helmet is provided, so hop on with that risk in mind.
If you're a solo traveler, moto would be good choice. It's cheaper than tuktuk, and faster as well. The going rate is between $6 - $8 per day.
PS. Although theoretically foreigners are not allowed to rent motorcycles, there is a tour company that does that. You can find out about dirt biking from Hidden Cambodia Adventure tours.

Tuktuk
By far the most popular choice of Siem Reap and Angkor transportation.
A tuktuk is a motorcycle pulling a hooded carriage. Some can fit only 2, some others up to 4 (or more if you can squeeze yourselves in).
It is comfortable method for exploring the area. The cushion is comfortable, you can put your feet up if you're really tired, and lean back and just enjoy the sights. The hood is also a big plus, because it protects you from the hot sun or the pouring rain.

Some tuktuks also have plastic 'doors' and 'windows'. Most of the time they are rolled up to keep them out of the way, and pulled down only when necessary. The plastic barrier comes in several sections, but they all zip up together nicely.
This feature could be particularly useful when it's raining outside or if you find the wind and dust are just too much.

Tuktuks usually cost $10 - $13 per day, and drivers usually charge few dollars more for longer distances. For a short ride to town, it' usually 2000 Riel - $1 per ride.
Also, you won't have a hard time finding an empty tuktuk. Tuktuk drivers fully anticipate Siem Reap tourism to increase, so their number seems to increase as well. Some even have a website that you can book in advance, like Mr Pik Savuth at Angkor Tuktuk, or Mr. Sotheara, at Angkorwat Driver.
Taxi, Car or Van

You can also rent a car or a van to get around. Although they are a bit of an overkill for short distances, I wholeheartedly love them for long distances.
If you plan to go to Phnom Kulen, Kbal Spean, Banteay Srei or Beng Mealea, you might want to use a car or a van. Those Angkor temples are rather far for a tuktuk ride, and the roads aren't exactly tuktuk friendly, ie. bumpy roads and dust particles flying around.
A car /van should cost $20 - $30 per day, depending on the distance. At this point it helps if you can find other people to share the ride.

So In Short...
Getting around Siem Reap is tremendously easy. Traffic isn't so bad either, merely regular slowing downs and stops at the lights.
It is still such a small town, that you can get from point A to point B in five minutes, and reach faraway Angkor temples without traffic. There is no stress at all in regards to traffic, but be forewarned that sometimes drivers go around a bit recklessly. This could look a bit alarming, but since all drivers are used to driving style, it seems they get around just fine.