OMG, there are TONS of Pokemon that need better sets.
Let me start with starters:
Snivy - some non-grass moves, idk. Dragon Pulse, EQ, Rock Slide, ExtremeSpeed, perhaps? Dragon Dance and Sleep Powder would totally own.
Oshawott - It's movepool is so terrible >...<" I'd give it Ice Punch, EQ, Superpower/Close Combat. Same as Forever, I'm disappointed it doesn't have CC, it deffo should.
Tepig - more fighting moves! Arm Thrust is just so bad... I know it gets some moves from TMs, but that's not that I want, srsly. Mach Punch, plox!
Sawk/Throh - more non-Fighting moves in their learnsets. A priority would be neat as well. Elemental Punches would own as well.
Zorua and Zoroark - lvl up Sucker Punch, wider Physical moveset.
Woobat - Trick, Baton Pass. CM Passing, anyone?
Excadrill - Iron Head
Ice cream family, Klink family - wider movepools! Vanistuff can't do much even with better movepool but what they have is just crap tbh. Klink has a Dragon Dance+ move that is, unfortunately, useless, because it doesn't have the moveset to fit it. Rock Slide, EQ are must. I'd also give it Flare Blitz - it could spin so fast and cover in flames. Or Overheat at least?
Seismitoad - no Ice moves? Dafuq?
Elektross - Elemental Punches. It's special movepool is great, but it's Physical is disappointing, especially, if it can use coil.
Golett - same as Elektross - Elemental Punches. It also needs Bullet or Mach Punch and Drain Punch. Iron First abusing FTW!
Deino family - Dark Pulse and Sucker Punch in lvl up
Now, non-native monsters:
Flareon - Flare Blitz, base Attack just begs for it!
Lucario - Doom Desire. I wouldn't use that but it would be cool XD
Sunkern - Implosion, Suicide, 0% Acc SelfDestruct, whatever. I hate that Pokemon so much :3c
That's pretty all for now. When more Pokemon will be know I'll post my hopes. I didn't mention many Pokemon with terrible movesets, like Audino or Pidove, but that's because I don't really care about them.