How to add thumbnail to an article in Joomla?

Is there any extension that helps me to add a thumbnail manually to an article?
Not those exts which do it on the fly using the first image in the article.
I want to add it manually.

Answer

See related question.

Look at there 2 components, you can achieve pretty much the same thing:

1. K2
2. ZOO, from Yootheme

I was a big fan of ZOO, but lately I became fan of K2.