Sketching and note taking are among the most important tasks I perform on my iPad. Unfortunately both this activities are almost impossible without a pen, even on your iPad. I have tried 3 different pens, so far, and I want to share with you my experience and preference.
The first pen I tried was Pogo Sketch Stylus (8$-15$)
This pen works fine, but it is not very precise. The tip has a squared edge and it is made in a spongy material. The shape and the size makes it hard to get a precise stroke.
The building quality is extremely disappointing. I would be surprised if it cost more that 50 cents to manufacture. The clip broke after a week, and the rest of the pen slowly fell a part within a month.
My second pen was a DAGi P501 (23$)
DAGi has a very original design. It allows an extremely precise input, since the tip is completely transparent, with a red dot that indicates the exact location of your input. This pen is well manufactured. Unfortunately I couldn't effectively use this pen, because it requires you to keep the pen at an angle, which is probably ok for sketching, but completely unnatural for tacking notes.
If your purpose is sketching, you may still want to try this pen. Watch this interesting video review on YouTube for more insights.
The last pen I tried (and love) is the Capacitive iPad Stylus by BoxWave (20.95$)
This pen is perfect for taking notes and rough sketching.
The pen works very well, and has a very sturdy body. It is completely made of aluminum, which makes it a very strong and light pen.
For 7$ more you may want to consider their Capacitive iPad, which is very handy when you are in a meeting, just carrying your iPad, and someone gives you some handout that you want to mark.
Enjoy you pen and your iPad!