Observant Jews say a blessing (Kiddush) over the wine that opens festive meals each Sabbath and on holidays. The Kiddush is also recited at the closing of the Sabbath in the Havdalah ceremony. This blessing may be said using any cup that holds at least a revi'it (about 76 ml) or according to other authorities, 150 ml. However, it is customary to use a specially decorated Kiddush cup made for this purpose. The cup may be made of porcelain, pewter or silver. Silver or silver-plated cups are generally washed with gold on the interior. Observant Jews need at least two such cups, since it is best to use a special cup for Passover. Some also use a separate Havdalah cup that may be part of a Hadvalah set.

What is a Kiddush ?
Kiddush is performed at the beginning of Jewish Sabbat and Jewish festival meals. The purpose of the kiddush is to remind Jews of the sanctity of the day, one must "remember it" by making arrangements specifically through the kiddush ceremonty.
It is customary to put the wine or grape juice used in the kiddush ritual into a decorated goblet called a kiddush cup. Kiddush cups are often given as gifts at a child's bris, bar-mitzvah, bat-mitzvah or wedding.

Friday night kiddush (english trasnlation):
The sixth day. And the heavens and the earth and all that filled them were complete.

And on the seventh day God completed the labor He had performed, and He refrained on the seventh day from all the labor which He had performed. And God blessed the seventh day and He sanctified it, for He then refrained from all his labor - from the act of creation that God had performed.

Permit me, distinguished ones, rabbis and colleagues:

Blessed are You, the Lord our God, King of the universe, Creator of the fruit of the vine. (Amen)

Blessed are You, Lord our God, King of the universe, Who sanctified us with His commandments, and hoped for us, and with love and intent invested us with His sacred Sabbath, as a memorial to the deed of Creation- a day preceding even those sacred occasions commemorating the Exodus from Egypt. For You chose us, and sanctified us, out of all nations, and with love and intent You invested us with Your Holy Sabbath.

Blessed are You, Sanctifier of the Sabbath. (Amen)

Selecting a Kiddush cup

1. Find a Judaica store online or offline. It should be a store that has a good reputation. Ask your rabbi or other knowledgeable people for recommendations. Compare prices between stores for cups of the same quality and weight.

2. Ensure the cup holds at least 150 ml or 76 ml according to your practice. 150 ml is an average sized cup.

3. Choose a distinctive and decorative kiddush cup. Select a special cup that does not look like an item you would use during the week.

4. The Kiddush cup should come with a matching coaster or base. This is important in the Havdalah ritual at the end of the Sabbath..

5. Try to select a quality cup that doesn't tarnish easily. Ordinary silver cups tarnish easily and need to be cleaned and polished.

6. You will probably want additional cups for Passover use, for Havdalah and to use as gifts.

7. Several online stores such as aJudaica.com offers wide selection of quality kiddush cups in low prices.