What is the longest 1×x brick ever released?
If you mean specifically Lego bricks, I'm pretty sure the 1x16 was/is the longest one made. Outside of the 1x? sized bricks, the longest plain shaped brick that I know of is part #30072 or #47122 at 24 studs long.  I don't know about other brands though.  

Interesting related post:
What is the largest single LEGO piece?