I'm no Peach expert by any stretch of the imagination, but I've heard people talking about how good of a team Peach/Sheik is. They have a lot of quick, strong hitboxes that can make for some wonderful volleyball. Also, like, half of GRSmash's Top 10 Team Combos is Armada/M2K craziness, so there's that. Take what I'm saying with a grain of salt emote, though, because I'm bad and I might not even know what I'm talking about. Maybe if there were some definitive resources for doubles, we could have more discussion about this kind of stuff, but... *sigh*
EDIT: I forgot to mention Falcon, he can get people off stage really easily and Peach can go for the gimp way deeper than Falcon ever could, and her turnips can save him from hell, especially on Dreamland.