Ropes:
There are many kinds of ropes differing in material and diameters which can be used for bondage.

Cotton: Cotton-ropes tend to unravel at their ends.
It's easy to clean them by simply putting them into the washing machine. Use some conditioner to make them a bit softer. Cotton rope is my prefered tool for Bondage, I actually use 1/2" diameter high quality 70% cotton/ 30% nylon mix sailing ropes. They are extremely strong, soft, and durable.

Nylon: Knots are easy to be unfastened. The ropes ends can be melt and therefore are more stable. Not as soft as cotton ropes and a bit stiffer.

Kevlar (carbon fibers): Soft ropes. Easy to loosen knots, ends can be melt, quite expensive. This stuff is great if you can afford it. 

Hemp: Hemp-ropes are cheap to buy, but it's a rough and stiff material. I personally find hemp ropes to be too abraisive and damages the skin quite easily.

Other Material used for Bondage

Handcuffs: Handcuffs are quite useful for a quick bondage. But due to the material there are a few problems. The wrists can be cut easily or nerves can be hurt. They are also not suitable for people with allergies, esp. Nickel or Chrome.
Handcuffs are not to be used if you want to hang the passive from a hook.
Keep your Hands off cheap cuffs as those might be a risk for the lack of safety. 

Leather and steel cuffs:  Cuffs made of leather or steel can be found in many variations, with or without padding. They are easy to lock and open and and they spread the pressure equally since they are quite broad.
If you buy them, make sure that the leather is well crafted and not too stiff, leather can cut like a knife. It would be better to spend a bit more money when buying the cuffs than to regret it later.
There are special ones for suspension bondage - don't use standard cuffs for that! 

Straps:  Straps and buckles can be bought in most any home improvement store or Outdoor Shop in different sizes. One of their advantages is the universal and easy usability combined with the possibility of quick removal. 

Chains: Bondages made of chains may look really great, but because of the material's stiffness and hardness there may be some problems. Also for persons with allergies, take care that the chains are well-finished so that the passive does not get cut. Be careful not to fix the chains too tight as it might hurt the passive.

Transparent Foil:  Also known as mummification. Keep in mind that the heat will stay beneath the foil. As a result, the passive may dehydrate if you use the foil for a long period of time. Give the passive plenty of liquids to drink to prevent dehydration, and remember to make sure that your partner does not develop problems with breathing. 

Do not use the following for bondage:

Cable Ties:  Cable ties can easily cut your skin because they are quite narrow.

Duct-tape: Tape can easily hurt the skin when removed and you won't be able to remove it fast enough in any case of emergency. It can also cause allergic reactions. 

Silken scarfs: Knots in scarves are very difficult to loosen. Use them to blindfold your partner but not for any kind of bondage. Remember, just because you saw it used in a movie does not mean it is a good idea.

Clothes line: Too stiff, too thin, cuts the skin easily. Knots can be difficult to remove once they tighten. This is the material I see many novices use and end up causing severe damage to their playtoy.