(1) Definitely, Maybe: Because it had the same premise as How I Met Your Mother, a very nice storyline, and because Isla Fisher is out of this world gorgeous.
(2) Sleepless in Seattle: Because Tom Hanks is incapable of making a bad movie, the little kid was hilarious, and there are very few things better than late 80's-early 90's Meg Ryan.
(3) When Harry Met Sally: See #2 regarding Meg Ryan, and a certain scene that she definitely "nailed" (no pun intended). Because it thoroughly explored the differences between men and women, had sharp and witty dialogue throughout, and because "I'll have what she's having" is one of greatest movie lines ever.
(4) Ghost: No explanation needed everybody loved Ghost
(5) Father of the Bride: Definitely my favorite of all of them because it has it all: Funny, great story, the bride is hot, good music, and most importantly by the end of the movie, you genuinely feel for these characters.