Usually or too often (at least in my experience), when I play Terran against Protoss I see that a Protoss player unattanded doesn't build a gateway army in the beginning and invests a lot in Robo-units (immortal, colossus) that are usually deadly for Terran.
Good treatment for that is an early push with marines/marauders. You can research Concussive Shells very quickly and marauders will wipe out zealots pretty quickly. However, you can't research Stimpack quickly, and if Protoss has some stalkers and few zealots, it's easy to lose your marauders: marauders will slow down zealots but will be killed by the stalkers. Also, you need to micro your units very attentively just to keep them alive a little bit longer while the Protoss player can just command them to attack and go back to macro.
So an early push without stim-pack doesn't look so attractive: you can lose your marauder army without any significant benefit. Okay, maybe you forced the Protoss to build stalkers/zealots that he probably didn't plan, but if he still has his army and you don't, this isn't of much benefit to you.
Would it be better, then, to postpone a push until Stimpack has been researched? Is there any effective way to push against Protoss as Terran before Stimpack?