On Dannyalcatraz's suggestions:
-If your players are fine with the flavor and general mechanics of the d20 Modern classes, but are just unhappy with the power level, then this is a nice way to go. It takes the d20M magic rules and provides a bunch of new options and classes that expand upon them. That said, save DCs will always remain fairly low with the advanced-class spellcasting model. You might want to just give all casters a small bonus to save DCs to compensate.
-Don't buy Dark•Matter for the magic. The spells and powers are skimpy and entirely reprinted from D&D books such as the PHB2. (In fact, the entire book is essentially a big reprint--albeit of a very cool pre d20 campaign setting).
-The Psychic's Handbook is pretty good, and I've used it in my Dark•Matter campaign without any problems (though I substituted a mana system for the nonlethal damage that the book uses). But it's unquestionably a Psychic book, rather than a magic book. The Advanced class it provides is pretty uninspiring, but the book is especially great for giving otherwise mundane characters one or two psychic options.
-I don't think True Sorcery is actually for True20--That's just an unfortunate name choice if I remember correctly. Don't have any actual experience with the book, though.