Hahaha, Doubles movesets for the Dynamic Duo, huh...?
Hmmm, okay, I think I have a good one. The point of these two is for Minun, the defensive one, to support and Buff Plusle, the offensive one, and I think I have just the solution!
Swift / Grass Knot (Swift for never-miss damage, or Grass Knot for dealing with your weakness)
Thunderbolt (Strong reliable STAB)
Nasty Plot (Blast that Special Attack nice and high!)
Sweet Kiss / Signal Beam (Sweet Kiss for confusion and time for Nasty Plot, or Signal Beam for damage, coverage, and a similar effect)
Helping Hand (Use this to support Plusle when he's ready to sweep)
Light Screen (Support both of your Special Defenses)
Trump Card / Thunderbolt (Trump Card for Drawn-out, but very powerful damage, or Thunderbolt for Reliable, consistent STAB)
Charm / Encore (Use Charm to help with Defenses, or Encore. Plusle and Minun are fast, so Encore is easier to use on them)
Plusle has to make massive amounts of damage to cover for Minun's support, and Minun has to support so that Plusle can continue to carry its weight.
These two are useless on their own, but together, with Plus, Minus, Nasty Plot, and Helping Hand, make for devastating attacks, capable of downing almost anything that STAB thunderbolt / Thunder can hit.
Minun is often preferred on its own, because of the Defenses, and the support it can give in any Double battle. Still, both Plusle and Minun, are best with each other.
It's like Randy Newman once said:
"One without the other, don't mean nothin' to me."