Well, I used Balsamiq Mockups for a pretty long time. It is pretty solid. However, after I switched a year ago from Photoshop to Sketch, I also do all my wireframing in Sketch. There are some wireframe-ui-components out there on sketch resources or other sides.

But sketch is pretty good for wireframing. You can make your own components / symbols, for reuse. And you can export it fast to marvel or invision to build a prototype.

But often, I also use oldschool pen & paper prototypes / wireframes. Its way faster to sketch it out on paper.

For "wire" like wireframing, paper is a good start. Google docs is very sufficient for diagrams (New -> Drawing), and supports collaboration. There are also a number of chrome apps (Gliphu, Cucoo, ...) that interoperate w/ google docs. I've tried a few, but fall back an a Google Docs Drawing 99% of the time.

pen an paper is the simplest