There are many, many other hadith about the benefits and blessings of Dhikr such that it is impossible to quote all of them here.
From the Sayings of Imams and Scholars about Dhikr
Ibn cAbbas (r) said "Allah, Almighty and Exalted, put a limit on all the obligations that He ordered human beings except for Dhikr. For it there is no limit."
Ibn Qayyim al-Jawziyya said in his book, Al-Wabil as-Sa'ib, p. 52, "There is no doubt that the heart oxidizes, just as copper and silver oxidize. Its polishing is the dhikr, which will make it like a white mirror. The oxidation of the heart is due to heedlessness and sin. Its polishing is by means of two actions: repentance and dhikr. If someone's heart is cloudy, the reflections of images will be unclear, he will see falsehood as truth and truth in the image of falsehood (batil). When there is too much oxidization on the heart, the heart will be darkened, and in the darkness the images of the Truth and Reality never appear. The best way to polish it is through Dhikrullah."
Ibn cAta'illah as-Sakandari said, "By Dhikr you leave behind heedlessness and forgetfulness, and you keep your heart Present with Allah, Almighty and Exalted. The best way to approach His Presence is by reciting the name 'Allah,' in the heart or on the tongue, or by reciting any of His Names." [Miftah al-Falah, p. 4]
Abul Qasim al-Qushayri said, "Dhikr is the strongest support in the way of Allah, 'Azza wa Jall. No one can reach the Divine Presence except by continuing to recite Dhikr." [Risalat al-Qushayriyya]
Mulay al-cArabi ad-Darqawi said, "Do not say, 'I am nothing'; neither say, 'I am something.' Do not say: 'I need such and such a thing'; nor yet: 'I need nothing.' But say: 'Allah,' and you will see marvels." [Letters of a Sufi Master]
We see from what has been mentioned that all guides and perfect shaikhs advised the seeker in the Way of Allah to make continuous dhikr in all states of their lives and to keep the company of the people in associations of Dhikr. We see that the Holy Qur'an and the Sunnah of the Prophet (s) and the scholars are all in accordance on this matter.
The Types of Dhikr
Dhikr can be can be done both silently or aloud. The Prophet (s) encouraged people to do both kinds. Among the scholars of shari'ah and the Sufi shaikhs, some preferred the loud dhikr and some preferred the silent dhikr.
Loud Dhikr
Bukhari narrated that Abu Huraira (r) reported that the Prophet (s) said, "If My servant mentions Me in himself, I will mention him in Myself. If he mentions Me in a group, I will mention him in a group in My presence." We understand from this hadith that to mention Allah in a group indicates loud dhikr. Some scholars determined from this that using loud dhikr is permitted.
Bukhari narrated in his book of hadith, that Ibn 'Abbas (r) said, "In the time of the Prophet (s) the people used to raise their voices in Dhikr."
Bukhari narrated in his book of hadith, that Abu Ma'bad (r), the freed slave of Ibn 'Abbas (r), said: "Ibn 'Abbas told me, 'In the lifetime of the Prophet (s), it was the custom to celebrate Allah's praises aloud after the obligatory congregational prayers.'" Ibn 'Abbas (r) continued, "When I heard the Dhikr, I would know that the congregational prayer had ended."
Imam Ahmad, Abu Dawud and Tirmidhi related that as-Sa'ib (r) preported that the Prophet (s) said, "Jibril came to me and ordered me to order my Companions to raise their voices in takbir."
It is narrated by Bukhari and Muslim and mentioned by Jalaluddin as-Suyuti, from other collections, that 'Ali bin Abi Talib (r) said, "I asked the Prophet (s) one time, 'O Messenger of Allah, guide me to the shortest way to Allah's Presence, and the easiest way to worship, and the best way for Allah, Almighty and Exalted. The Prophet (s) said, 'O 'Ali, you have to be continuously making Dhikrullah, silently and aloud.' I replied, 'O Prophet (s), all human beings are making dhikr. Give me something special.' The Prophet (s) said, 'O 'Ali, the best of what I, and all prophets before me, said is, la ilaha illallah. If all the heavens and earth were placed on one side of the balance and la ilaha illallah were placed in the other, la ilaha illallah would be heavier. Judgment Day will never come as long as there are people on this earth saying la ilaha illallah.' Then I said, 'How should I recite.' The Prophet (s) said, 'Close your eyes and listen to me reciting la ilaha ill-Allah three times. Then you say it three times and I will listen to you.' Then the Prophet (s) said it and I repeated it in a loud voice."
In the narration of Imam Ahmad and Tabarani this hadith is continued, describing how the Prophet taught his Companions the dhikr. "'Ibada bin Samit said that the Prophet (s) said, 'Is there any stranger among you?' And we said, 'No, Ya Rasul-Allah.' He said, 'Close the door.' Then he said, 'Raise your hand and repeat after me La ilaha illallah' We raised our hand and said, la ilaha illallah. Then the Prophet (s) said, 'Praise be to Allah that He sent me to this world with this kalimah, and He ordered me with it, and He promised me the Paradise with it, and He never changes His Promise.' Then the Prophet (s) said, 'Be happy! Allah has forgiven you.'"
Jalaladin as-Suyuti mentioned in an article called "Natijat al-Fikr fi Jahri-dh-Dhikr," the Benefits of Loud Dhikr, twenty-five authentic hadiths which mention doing loud dhikr.