However after reading a few articles on creating mock ups, I'm getting the impression that it is potentially a very wasteful process.
For the ultimate whiteboard - functional public site design process, thinking through the best IA and wireframing things out before creating mockups, settling on one, then coding is the best way to go.
However, for time efficiency, it depends how you conduct your client relationship and what sort of websites you're pumping out.
Are these quick brochure sites for a few hundred each, or $1 - $3k custom sites? Or a few hundred dollar small brochure sites where the client would be happy just using a given wordpress theme?
When I ran a web design company a couple years ago, our process was to gather as much information as possible about the necessary features and content, letting us determine the IA, and as much as possible about what sort of design they wanted, the look and feel they were going for, and we'd often ask that they link us a few websites they like, and explain what it was they liked, whether it was the layout, the color scheme, the over all visual tone, etc.
From there, I'd whip open photoshop and design a mock up of something for them. This part, if anything, allowed us to create better work, and have happier clients. Any changes to layout / design they wanted could just be redone in photoshop, quickly. It wasn't until they were settled on the layout and design that we started coding, generally into WP. Sometimes they'd want some small layout revisions after we had started coding it, but mostly, the compositions saved us from having to back track further.
Depending on the site, sometimes it's easier to do a photoshop composition first anyhow. Even if you aren't showing it to someone.
If you really want to skip the mock up portion of the process, then your best route would probably be to gather a few different themes for brochure sites or ecommerce sites, and present them to clients asking them to choose one and giving them the option of certain layout changes.
A lot of it really depends on whether or not they want a unique design and heavily branded site, or something pretty generic with their logo and color scheme and some photos of their own.