You asked me to talk about: That trope you wish more people would write/would pop up in the canon proper.
Tropes I wish more people would write are my favourites, like amnesia-fic, AMTDI, mind control, space pirates, and drunk/stoned characters. And tentacle-fic. Oh, and sex pollen, I do love sex pollen! And robots - love a good android story :D. But I can't say that I'm missing out on them in SGA, which lends itself to every imaginable trope because canon went there at some point (well maybe not all the sexy, kinky tropes, but still) - it's one reason I still love SGA. There's less of some of these tropes in due South, although canon still ranged remarkably freely (space androids!) and people have been very creative with the incorporation of voodoo. In Sherlock - not sure? The wilder tropes I've read have been more urban fantasy but there's definitely Sherlock sex-pollen and tentacle fic - some of it very dark and disturbing from the look of the tags, unlike most of the SGA stories (*is a fine one to talk: has written SGA tentacle darkfic*). Mythbusters has some good android-fic, but is otherwise a little constrained by canon from the wilder realms of my trope-faves. The Losers - there's a little of the above, but again, canon means the fics need to be very AU to accommodate these tropes. Overall - more of all the above please, but especially sexy tentacles!
In terms of favourite tropes actually in canon in my fandoms, good old SGA probably has the most. It's got amnesia, it's got androids (replicator team), it's got AMTDI and mind control but sadly not the sexy kind, just the H/C kind. I don't think there are tentacles (I'm not counting Chaya's glowing tendrils), but the travelers are definitely space-pirates. I don't recall any spectacularly drunk/stoned eps either - none that were fun, anyway. And there's even less of all that in the other fandoms. So plenty of missed opportunities there in canon - but then, that's what fanfic's for, of course. *grin*
If you can think of any canons heavy on a few of my favourite tropes, do let me know!