Knitting Needles, double pointed needles and even more needles
For every type of yarn, there is a needle and here are a few tips, pun intended.The thicker the yarn, the larger the needles should be. One of the latest fads in knitting is using HUGE needles to create a chunky project quickly. Size 50 needles or eve size 75 needles will give you a large knit and project with very few stitches.
But size isn't all that matters. The sharpness of the tip of the needle will help or hinder you as you move through your project. A knitting needle with a very sharp tip should be used for single or double ply yarns. Yarns which are smooth and silky feeling; a sharp needle will reduce the chances of splitting and fraying the yarn and will keep your finished project smooth and silky also.
A needle with a blunt tip is idea for wools, wool blends and fun yarns; yarns with fur, loops and glitter. The blunt needle will pass smoothly through the frayed pieces and loops without altering the unique texture of the yarn.
And finally; finials. I love these needles; they are beautiful but personally, I have a very hard time with them. My knitting travels with me, so stitches fall off these needles in my bag and I spend a great deal of time picking up what I've dropped. I love to use these needles at home on a non-traveling project.
So for me, a needle with a large finial or nob on the end which prevents my stitches from slipping off the back is ideal.
As to the difference between wood and metal that is completely a personal preference. I use both and love both but do change them up depending on the project and the weather. In the summer, I prefer metal needles because I live in the Midwest where it is warm and humid and that weather combined with the oils, heat and pressure of my hands makes my wooden needles very pliable. This also makes them ideal for me for the winter.
The biggest deciding factor for me in choosing a wood or metal needle is if I will be doing a decorative stitch or not. I prefer to do cables and decorative stitches on metal needles to aid with the resistance in pulling stitches through, but again, this is my personal preference.
If you have any questions, need an exotic or HUGE set of needles or just want to try out a few different needles to see how they feel and which you prefer, hit your neighborhood yarn store; they will have everything you need. I once needed sizes 17 and 19 circular needles for a project- I thought it was a typo or a conversation error- I didn't even know those odd sizes existed until I went to my shop A Piece of Ewe.
So, find a needle you like, a yarn you love, and enjoy!