You can use wood, metal, or composite or a combination.

Wood Railing: You can use the same decking materials and handrail.  This is a classic look an everything will match.

Metal Railing: In metal there are many combinations you can do.  You can go with solid metal railing with metal posts, metal railing with posts that are composite or wood with a similar cap (the cap is nice play to set your beverage while you mingle).  You can also use wood or composite railing that has metal balusters.  If you do this you can use a variety of colors for your balusters to contrast or compliment your deck.

Composite Railing: With composite some caution is needed.  The top and bottom rails along with the cap are great and will last.  The composite baluster has some issues.  There have been issues with the balusters.  After installation and they go through some weather there is a tendency to crack and warp.  The best options when using composite handrail is to use metal balusters.  They can either be screwed on the outside or installed in-between the two rails.

Whichever way you decide to go, handrails add class to your deck.