I know I already wrote about my love of Mountain Pose, but here are some other favorites:
Tree: I really like this pose because it's all about balance. You stand on one foot, and have the other resting on the inside of your opposite thigh (or the side of your calf, depending on your flexibility). You slowly bring your hands from heart-center and lift them above your head and spread them out, like the branches of a tree. You really do feel like a plant, rooted in the earth and reaching for the sky. Plus, it's definitely an [evil] ego-boost when you can hold the pose while others are tipping over.
Warrior II: This is a pose that definitely makes you feel strong, much like a warrior. You are in a version of a lunge where your front leg is bent and holding most of your weight, and your back leg is straight, with the back foot perpendicular to the rest of your stance. Then your arms are held straight, one facing the front, the other pointing behind you. Your face is to the front, as if you're in a steady pose awaiting an attacker. Each limb is very sturdy in this pose, which can give you a lot of confidence (i.e. you're not likely going to fall out of this pose).
Downward Dog: This is a standard yoga pose that every yogi does. You're on all fours with your limbs straight, like the legs of a dog. Then you try to push your upper body towards the floor while your hips and tailbone reach for the ceiling. This is a pose to help strengthen your shoulders and stretch out your hamstrings. When I first started doing yoga, this pose was very hard for me to do. Now, my heels are completely planted on the floor (most beginners will be standing on the balls of their feet), which allows for a deeper stretch. I feel like this is the pose that will let you know if you are improving or not; it doesn't matter how well I perform the other poses, but if I can feel that I'm getting deeper into my Downward Dog, then I know I'm getting better.
Here is a great graphic of beginner yoga poses: http://www.superskinnyme.com/yoga-poses-for-beginners.htm