If we are commanded to marry, why no bracha "sanctified by your commandments". (Marriage is #70 on Rambam's list of mitzvot, see: http://www.jewfaq.org/613.htm.)
After the beracha over the wine, the officiant says the birkat erusin:
ברוּךְ אתּה י-י א-להינו מלךְ העוֹלָם אשׁר קדשׁנוּ בּמצוֹתיו וצוָנוּ על העריות ואָסר לָנוּ את הארוּסוֹת והתּיר לָנוּ את הנשׂוּאוֹת לָנוּ על ידי חפּה וקדוּשׁין. בּרוּךְ אַתּה י-י מקדשׁ עמוֹ ישראל על ידי חפּה וקדוּשׁין
Praised be Thou, O L-rd our G‑d, King of the universe who has sanctified us with His commandments and has commanded us concerning illicit relations; and has prohibited us those who are merely betrothed; but has permitted to us those lawfully married to us by chuppah and kiddushin. Blessed art thou G‑d, who has sanctified His people Israel by chuppah and kiddushin.
Translation from Chabad.org
As you can see, there actually is such a beracha as you are asking about said at a wedding.
Some additional information from that same page:
With His Commandments. The Rabbis pondered whether this blessing could technically be classified as birkhat mitzvah (a blessing that precedes the performance of a mitzvah), as the blessing over the shofar, for example. The predominant opinion held that it could not be so classified, since the mitzvah is not completed until after the couple had conjugal relations. In any case, the mitzvah did not depend on him alone, and the bride had not yet formally consented. Nonetheless, the Sages could not bring themselves to exclude such a mitzvah from having a blessing. Thus they instituted a special blessing for the sanctification of the Jewish people for practicing marriage that was properly authorized by the law.
So while there is indeed a beracha that includes "sanctified us with His commandments," the majority of rabbis hold that it is not actually a birkat mitzvah for the reason stated above.