7x03 Cheaper by the coven
A reference to the book "cheaper by the dozen" which has also been made into a movie.

7x04 Charrrmed!
The three "r"s in the title refer to the 3 Charmed Ones.

7x06 Once in a blue moon 
Once in a blue moon is a common saying to express that something happens seldom.

7x07 Someone to witch over me
Refers to the song "Someone to Watch over Me" - words by Ira Gershwin, music by George Gershwin. Introduced by Gertrude Lawrence in the stage musical "Oh, Kay!" 1926.

7x10 Witchness protection
A play on the term "Witness protection"

7x12 Extreme makeover: world edition
The title is based on the show "Extreme Makeover: Home Edition" where a group of people totally remake someone's home.

7x13 Charmageddon
It is a play on the word Armageddon.
Armageddon in Christianity is anticipated as the final battle between the forces of good (Jesus and his angels) and the forces of evil (Satan and his demons).
It also refers to any great loss of life in battle etc.

7x14 Carpe Demon
A play on the phrase "Carpe diem" which is Latin for "pluck the day," meaning "enjoy the moment".

7x15 Show Ghouls
The title is a mix of Ghosts and Souls and maybe also a reference to "Showgirls"

7x16 The seven year witch
The title is a reference to the 1955 movie "The seven year itch"

7x17 Scry hard
The title is a reference to the movie Die hard, a movie in which one "forgotten" guy ruins the plans of the villains.

7x18 Little box of horrors
The title is a play on the movie Little shop of horrors

7x20 Imaginary fiends
The title refers to the term "imaginary friend".
A fiend is among others one of the evil spirits of traditional Jewish and Christian belief

7x21 Death becomes them
The title is a pun on the movie "Death becomes her"

7x22 Something wicca this way goes
The title refers to 1x01 Something wicca this way comes

8x01 Still Charmed and kicking
The title is a reference to the phrase "alive and kicking".

8x02 Malice in Wonderland
This is a reference to the classic novel, "Alice in Wonderland".

8x03 Run, Piper, run
Could be an allusion to "Run, Lola, Run" or to the song "Run, Rabbit, Run", which was written by Noel Gay and Ralph Butler for Flanagan and Allen. Bud Flanagan sang it in the musical "The Little Dog Laughed".


8x04 Desperate housewitches
This is a reference to Desperate Housewives, the wildly popular ABC series.

8x08 Battles of the hexes
This is a reference to the common phrase "battle of the sexes". The phrase was also used as the title of the 1959 Charles Crichton film "The Battle of the Sexes", starring Peter Sellers.

8x09 Hulkus pocus
This is a reference to the comic book character "The Incredible Hulk" which was also made into a TV series and a film. Plus it's also a reference to the common witch phrase "hocus pocus" referring to magic - which was also a film, "Hocus Pocus" starring Bette Midler, Sarah Jessica Parker and Kathy Najimy.

8x10 Vaya con Leos
This is a reference to the Spanish phrase "Vaya con Dios," which is a common farewell phrase which literally means "Go with God".

8x11 Mr. and Mrs. Witch
This is a reference to the 2005 film "Mr. & Mrs. Smith", starring Brad Pitt and Angelina Jolie as rival spies who also happened to be married.

8x12 Payback's a witch
A reference to the common saying "payback's a bitch".

8x13 Repo Manor
This is a reference to the 1984 film "Repo Man".

 

8x14 Twelve angry Zen
This is a reference to the classic 1957 film "12 Angry Men", starring Henry Fonda as a dissenting juror in a murder trial.

 

8x15 The last temptation of Christy
This is a reference to the 1988 Martin Scorsese film "The Last Temptation of Christ"

8x16 Engaged and confused
This is a reference to the 1993 film "Dazed and Confused" about a group of high-schoolers on the last day of school in 1976. "Dazed and Confused" is also a 1969 song by Led Zeppelin, who also use the triquetra to represent their band. The song was later used as the basis for the title of the film mentioned above.

8x17 Generation hex
This is a reference to the phrase "Generation X".
Generation X is a term for the generation of people born in the Western world following the post-World War II baby boom generation.

8x18 The Torn identity
This is a reference to the best selling book "The Bourne Identity" by Robert Ludlum, which was adapted into a 2002 film "The Bourne Identity" starring Matt Damon about a man recovering from amnesia only to discover he is an assassin.

8x19 The Jung and the restless
This is a reference to the daytime soap opera The Young and the Restless.
It also refers to Carl Gustav Jung (26 July 1875 – 6 June 1961), a Swiss psychiatrist and founder of analytical psychology.

8x20 Gone with the witches
This is a reference to the famous 1939 film "Gone With The Wind" about Southern belle Scarlet O'Hara, that was based on the novel by Margaret Mitchell.
 

8x21 Kill Billie: Vol. 2
This is a reference to the 2004 film "Kill Bill, Vol. 2", starring Uma Thurman and directed by Quentin Tarantino. It's also a reference to an episode from earlier this season called "Kill Billie Vol. 1".

8x22 Forever Charmed
The title is a reference to the 1947 Otto Preminger film "Forever Amber"" and the 1944 novel of the same name by Kathleen Winsor.