It is narrated from Ibn Umar that the Prophet Muhammad (sal Allahu alaihi wa sallam) said:
There aren't any days greater, nor any days in which deeds done in them are more beloved to Allah, the Most High, than these ten days (of Zul-Hijjah). So, increase in them the saying of Tahleel (La Ilaaha illa Allah), and Takbeer (Allah Akbar) and Tahmeed (al-Hamdu li-llah)" [Musnad Imaam Ahmad]
1249. Ibn `Abbas (May Allah be pleased with them) reported: The Messenger of Allah (sal Allahu alaihi wa sallam) said, "There are no days during which the righteous action is so pleasing to Allah than these days (i.e., the first ten days of Dhul-Hijjah).'' He was asked: "O Messenger of Allah, not even Jihad in the Cause of Allah?'' He (sal Allahu alaihi wa sallam) replied, "Not even Jihad in the Cause of Allah, except in case one goes forth with his life and his property and does not return with either of it.''
Commentary: This Hadith brings out the following point: Righteous deeds during the first ten days of the month of Dhul-Hijjah are far better and more rewarding than righteous deeds done on other days of the year, because they are Hajj days in the sacred season of pilgrimage. Because of their excellence and importance, Allah (subhana wa ta?ala) swore by them, thus: "By the Dawn; by the ten Nights...'' (89:1,2)
Ten Best Days-Sheikh Yasir Qadhi : http://www.youtube.com/watch?v=pWixVC04yyU&feature=related
Virtues for the 10 days of Dhul Hijjah!!! : http://www.youtube.com/watch?v=YY2KO1nSP-c