Other Options: It can Swords Dance if you really want to. Leech Seed and Razor Leaf via tradebacks.
Verdict: Double powdering is always nice, but Vileplume's offensive capabilities are not exactly what you'd call "exciting." Since she doesn't pick up Razor Leaf without tradebacks from GSC, she is stuck with the confusion-inducing Petal Dance or the weakly powered-Mega Drain for a STAB move, and Body Slam is her only choice for attacking things that resist Grass. However, only with Swords Dance will that cause much damage, and using Swords Dance will be at the expense of Stun Spore. Vileplume is really cute, but she is probably inferior to every other Grass Pokemon in the game.
