I've tidied up and alphabetised the cliché list (OCD much?), tweaked, changed, and clarified some things, and added a few things I thought were missing, to bulk it up to a nice, round 50. Is it wrong that my aim is to do everything on this list at least once?

Also, I think this should be rebranded as tropes, rather than clichés, because it has a less negative connotation. IMO. I mean, yes, often they are clichés, but I've also seen them done well and interestingly. Or amusingly crackish. *g*

Bolded all those I've written, with links to the evidence:

1) Accidental/immaculate/alien pregnancy:
2) Aliens make them do it: Think Of England; Unlahfulliche in Lyhte
3) Alternative Realities: New Ground; Transparent; The ALTERNATE Alternate Universe; Ambition (the Mens Rea remix); All In A Good Cause; All To Myself, Alone; jack_built fics 1, 2, 3, 4, 5
4) Amnesia:
5) Angry!sex: Sometimes I Can Forget
6) Aphrodisiacs: Sugar For My Honey
7) Apocalypse / post-apocalypse: Not EVEN.;Wake Me Up When The Skies Are Clearing; Not Dark Yet (But It's Getting There)
8) Baby Farm: Think Of England
9) Bodyswap:
10) Brainwashing: Makin' Whoopee; N is for Nish'ta
11) Character Tortured to Secure Other Character's Cooperation:
12) Confined spaces: Out Go The Lights 1, 2, 3 & 4; Jam Jar; Safe And Sound
13) Cross-dressing: Blooper Reel
14) Curtainfic (characters in a domestic setting, such as buying curtains): Kissin' In The Back Row Of The Movies; P is for Peridot; Tiggers Like Everything
15) Deathfic: If You Gotta Go...; Peanut M&Ms And The Twinkle In Her Eye
16) Drunkfic:
17) Evil Twin: Maybe I'm An Angel Underneath
18) Forced to share a bed: The Mission After
19) Genderswap:
20) Ghostly intervention: Need To Know; Transparent
21) Going Rogue: Ambition (the Mens Rea remix)
22) Groundhog Day: Practice Makes Perfect
23) Hero Wrongfully Accused:
24) Holiday / celebration: One Fish, Two Fish; Pirating 101 and sequels
25) Huddling together for warmth: Into The Blue
26) Hurt/Comfort: Don't Have A Cow, Man; Planet Of The Woobies; Safe And Sound
27) Kidfic: Sam/Daniel schmoopy kidfic; Q is for Questions; To Dance On The Floor In The Round
28) Kidnapping:
29) Matchmaking Third Party: Valentines series
30) Medical Discharge:
31) Mistakenly assumed to be gay: What A World
32) Mpreg:
33) Near Death Confessions: If You Gotta Go...
34) Pretending to be married: Unlahfulliche in Lyhte
35) Secretly a virgin: (Rarely) Pure And (Never) Simple
36) Slavery: Float Like A Butterfly; Think Of England
37) Snowed in:
38) Space pirates: Living The Dream 1 & 2; OT4... or 5... or 6...
39) Stranded Off-World: Stepping Into The River
40) Talking to a Shrink:
41) Telepathic soulbonding:
42) Tent Porn: Fumbling Towards Ecstasy
43) Time Travel: Real People; all my Terminator fics
44) Truth or dare:
45) Turned into animals:
46) Turned into cavemen: Revisions 1: Conjecture
47) Undercover in a gay bar:
48) Wedding: Living And Learning
49) Werewolves mate for life:
50) Wingfic: Defying Gravity

So, I've done 26/50 - so far.

ETA: 28/50 (crossed off two with 'Think Of England').

ETA2: 29/50, 'Fumbling Towards Ecstasy'. And I've decided to remove "Mary Sue", because that's not so much a trope as an inability to write well, IMO. Instead, I've added in "Turned into cavemen". :)

ETA3: 30/50, with 'The Mission After', plus another kidfic one because that's what presses my buttons.

ETA4: 31/50, "pretending to be married", and another AMTDI.

ETA5: 33/50, "evil twin", and I just realised that I did "turned into cavemen" a long time ago, with an ep tag to 'Broca Divide' (oh Stargate, you've done most of these tropes already, bless you!).