Handcuffs?

[Ruby]

Rope is good.

Velcro cuffs are also very nice.
They are wonderful when the sub needs to quickly escape for a variety of reasons. And of course, they are great for self bondage. Simultaneously, they can make you feel helpless and trapped, because they require quite a bit of pulling and tugging for release.

Ties for men can also make excellent restraints as can womens scarves.

Click on the "Store" button on this site for some ideas.

I also like using chains, tied into slip knots. The chains give that metal feel, but are easier to remove from my sub.

If you don't want to shop online or feel funny visiting the local kink shop, you can go to home building stores, often called "dom-depots" in the US and stores that supply items for dogs and cats.