I have a few supplements for True20, but am not really familiar enough to offer any real recommendations.
For M&M2e, on the other hand, I'd recommend Instant Heroes, the Freedom City campaign setting and Ultimate Power. Each depends on what you plan on doing.
The FC setting is a plug-n-play setting, with plenty of NPCs and adversaries statted up, most of them extremely reminiscent of famous Marvel and DC characters, to create a very nostalgic feel, which can help to make the setting familiar, or distracting, depending on your tastes. If you don't have a specific setting in mind, it's a well-designed city, with a bit of a Boston feel to it (with dashes of NYC, as it, like most of the characters in it, is a collage of multiple sources).
Ultimate Power is a toolkit for do-it-yourself character building. If you aren't really into plunging hands-first into the guts of a system and getting grease on your overalls, you won't really need this. If you love that sort of thing, it's the bees knees. It's also horribly out-of-print. So out-of-print that the backup copy I ordered from Green Ronin almost two years ago still hasn't arrived. Pray for a reprint.
Instant Heroes has several dozen characters, following each of the various 'themes' like 'armored hero' or 'mystic master' or 'martial artist,' and then presenting at least *three* different variations on that character. And there's an appendix at the back that offers one of each of these archetypes at PL 6, for lower-powered games, or supervillain 'mooks' or whatever. If you've got your own campaign setting in mind, and Freedom City wouldn't be needed, I would rate this as number one.