I am an enormous fan of Wacom's products. For the last 15 years I have been using their tablet to draw via Adobe's Photoshop and Corel's Painter. Photoshop mainly.
Now with iPad I tend to find myself drawing digitally "on the go".
My pen of choice is the Wacom Intuos Creative Stylus. It's beautiful to use and offers 2048 levels of pressure sensitivity. Coupled with the awesome ProCreate app the drawing and painting experience is second to none.
The nibs on the Wacom CS pen are good but they will tear over time.
For replacement nibs look to the Wacom store at this link: http://uk.shop.wacom.eu/accessories/bamboo-stylus/bamboo-stylus-replacement-nibs/478
If you look at the compatibility for the nibs you'll see that the Wacom CS-500 series are supported.