From asimplejew blog. He has some amazing stuff on his blog.
One who regularly recites Tehilim eliminates all types of misfortunes and terrible tragedies from himself, his household, his family and his whole generation, and brings upon them every form of shefa, good blessings and successes. And there is nothing to shield against Mazikim, like the recital of Kaddish after Tehilim. (Pele Yoetz)
The Tzemach Tzedek says that Tehilim breaks all the barriers and ascends before the Adon Olamim, and works wonders with chesed and rachamim. (Kovetz Michtavim)
Through Tehilim, the final redemption is brought closer. (Pardes Menachem, Shir Hashirim)
Baba Sali would say that every Jew is required to complete Sefer Tehilim at least once a month, and that there is special significance and power in the words of Dovid HaMelech and they can work wonders. (Baba Sali, by Rav Eliyahu Alfasi)
As if Dovid HaMelech Himself is reciting the Words
David HaMelech wrote Tehilim with Ruach Hakodesh. (Likutei Mohoran 156) When one recites Tehilim, it is as great as if Dovid HaMelech, himself, is saying it. The Ruach HaKodesh is still in the words of Tehilim. When you recite Tehilim, your own breath arouses the Holy Breath in these words. Therefore, when you recite Tehilim, it is as if Dovid Hamelech himself is reciting it. (Sicos HaRan 98) In the Yehi Rotzon before Tehilim, we ask that our recital of Tehilim should be as if Dovid HaMelech himself is reciting it.
Tehilim Includes the Whole Torah
Dovid HaMelach put together Tehilim in five books, corresponding to the five books of the Torah. We find that the whole Torah is included and hidden in Tehilim. When Dovid HaMelech would suffer, he would look in the letters and words of that tzarah in the Torah and compose a chapter of Tehilim, which was revealed to him through the light of the Torah. And each chapter of Tehilim certainly corresponds to a chapter in the Torah. (Degel Machane Ephraim, Chaye Sarah)
The Yehi Rotzon, after reciting Tehilim, mentions this concept. It says the first book corresponding to Bereishis, the second corresponding to Shemos and so on.
Getting Rid of Mikatrigim
The author of Shaarei Orah writes that the main minhag of reciting Tehilim is order to chase away the mekatrigim before tefila, so that our prayers can go up without any kitrug. (Levush)
Yiras Hashem
The study of Tehilim brings one to Yiras Hashem. (Maharsha)
Teshuva
When Klal Yisroel recites Tehilim with a broken heart, Hakodosh Boruch Hu forgives all their sins. (Mayim Rabbim)
Ziknei Torah
Finding Oneself in Tehilim
Pidyon
Fulfilling the Whole Torah
Meriting being ??? ??? ?????
The last letters of ????????????? ??????? ????-?????-?????????? ????????????? (Vayigash 45, 13) spell ???? alluding that whoever recites Tehilim daily will merit being ??? ??? ????? (Rabbeinu Ephraim, Vayigash)
Segula for Rainfall
Reciting Tehilim is a segula for rainfall; ???? stands for ????? ?????? ????? ???? (Sefer Hamidos, Segula)
Meriting to go to Yerushalayim
The Whole Sefer Tehilim without Interuption
Parnasa
It is a segula for parnasa to recite any three chapters of Tehilim, specifically, after davening. (Reb Avrohom Moshe of Raspasha-Pshadvars)
Weapon against the Yetzer Hora
Reciting Sefer Tehilim three times in one day is like sword and spear against the yetzer hara. (Reb Menachem Mendel of Rimanov)
Like a Fast from Shabbos to Shabbos
There is a kabbala from the Rebbe, Reb Elimelech of Lizensk, that one who recites Sefer Tehilim three times in one day is considered as if he fasted from Shabbos to Shabbos.
Early Morning Tehilim
The last letters of ??????? ????-????????? ??????????? spell ????, because it is a choice mitzvah, to wrap oneself in tzitzis, early, and learn Tehilim. (Rabbein Ephraim, Vayishlach)
Tikun HaKlali
(I cannot do this subject justice here, but a post on Tehilim would not be complete without some mention of Tikun HaKlali.)
Reb Nachman said that of all his Torah he is sure but of this one he is even more certain. (Sichos HaRan 141)
Elul
It is brought down many places to finish the whole Sefer Tehilim at least 2 times before Rosh Hashana, since the gematria of ???, forgive, is 300, and there are 150 chapters of Tehilim, and to finish it a third time before Yom Kippur.
Chapter 119
For a sick person the same thing is done except the mothers name is used and after the name the words ??? ??? are added (instead of ????).
Sholom Bayis
A segula for sholom bayis is to spell out the words ???? ???? with chapter 119, everyday. (Segulas Yisroel)
Keeping Out of Gehinom
In Tehilim 25 each posuk starts with a different letter of the aleph beis, except the letters ????, which are the gematria of ??????. Therefore reciting chapter 25 every day is a segula not to go to Gehinom. (Found in many editions of Tehilim)
Woman in Labor
Arizal says that Chapter 20 is good to say for mercy on a woman in labor. It has 9 pesukim corresponding to 9 months of labor and 70 words corresponding to the 70 pains of childbirth. (Divrei Torah 3:30) The Chida says that one should say it 12 times and then say a special Yehi Rotzon. (Avodas HaKodesh)
Chapter 100 is a segula for a woman in difficult labor. The first letters of the opening words, ????????? ?????????, ???, are equal to 70, referring to the 70 screams of a woman before giving birth. There are also 43 words referring to the klipa of ??, which also equals 43, from the posuk (Malachim1 3:25) ?????? ??????? ????-??? ???-???? ??? ???????-????????. (Likutei Mohoran II 2, end)
Sweeten Harsh Judgments
Chapters 39 and 77 sweeten harsh judgments. (Sefer Hamidos, Hamtokas Din 37, 42)
Teshuvah
Chapter 51 is established on teshuva. (Noam Eliezer)
Harsh Decrees
For harsh decrees, that the nations decree on Yisroel, recite chapter 62. (Sefer Hamidos, Hamtokas Din, 53)
Haters
For Barren Woman
A segula for a barren woman to bear children is to recite chapter 102. (Likutei Mamorim)
Shidduch
In Asara Mamoros it says that reciting Chapter 121 at the end of all the tefilos, before stepping back, is a segula to find a good shidduch. (Igra D’Pirka 63) The source for saying Tehilim 121 is a Medrash that says Yaakov Avinu said this, praying to find his match. The first posuk says “From where will my helper (meaning wife) come?” And the next posuk says “My help will come from Hashem”.
One who is looking for a shidduch should say the following chapters of Tehilim: 32, 38, 70, 71, 124. (Segulas Yisroel)
Rescue from Enemies
Sleep
The 15 chapters of Shir Hamalos (120-134) are a segula to eliminate sleep. (Sefer Hamidos, Sheina 3)
Chapters 1-4 recited before going to sleep, are a segula to prevent mikra layla. (Shlah)
Victory
For victory recite chapter 12. (Sefer Hamidos, Meriva 37)
Chapter 67
Many seforim bring down segulas attributed to reciting chapter 67 in the form of a menorah. Some have it printed on parchment.
For Release of Prisoners
Many times in recent years Rabbonim have asked that Chapter 142 be recited for the release of prisoners, since this is what Dovid HaMelech said when he was trapped in the cave.
Corresponding to Age