Over the years I've collected quite of few design process diagrams that I like and use as reference to constantly iterate on my process. Here are some of my favorites.

Donald Norman's Double-Diamond Model

Reference: The Design of Everyday Things

Dan Nessler's Double Diamond Model

Reference: https://medium.com/digital-experience-design/how-to-apply-a-design-thinking-hcd-ux-or-any-creative-process-from-scratch-b8786efbf812#.rn1ouppjr

Design Council's New Double Diamond

Reference: https://medium.com/design-leadership-notebook/the-new-double-diamond-design-process-7c8f12d7945e

d.school's User-Centered Prototype-Driven Design Process

Reference: http://dstudio.ubc.ca/research/toolkit/processes/

Stanford ME310 Design Innovation Process

Reference: http://web.stanford.edu/group/me310/me310_2016/about.html

EffectiveUI: UX Design Process

Reference: https://medium.com/@effectiveui/the-ux-design-process-what-clients-need-to-know-d6ed00d0b977#.pjudgx82j

Objective-Based Design

Reference: http://www.dtelepathy.com/blog/philosophy/objective-based-design-creative-approach-to-solving-business-challenge
http://www.axure.com/c/blog/177-five-ways-ux-firm-digital-telepathy-designs-through-conversation.html

Vijay Kumar's Analysis-Synthesis Bridge Model

Reference: http://www.dubberly.com/articles/interactions-the-analysis-synthesis-bridge-model.html

Laseau's Funnel

Mentioned by Bill Buxton in Sketching User Experience

Reference: https://blog.prototypr.io/a-good-design-process-90ae32d31dcd#.otxowy83a

Engineering Design Model

From Engineering Design Methods by Nigel Cross

Reference: http://www.core77.com/posts/52948/Why-is-Sketching-Still-Important-To-Design

NodeSource's Digital Product Design

Reference: https://medium.com/@nodesource/what-is-digital-product-design-93caad4e4035#.vqd75mfoj

Paul Hershey's Process

Reference: https://medium.com/looks-good-feels-good/user-experience-for-product-designers-e9fa621ce3bc#.cr0xsi5l3

Nielsen Norman Group - Design Thinking 101

Reference: https://www.nngroup.com/articles/design-thinking/

Hang Guo's Spiral UX Design Process

Reference: http://www.uxmatters.com/mt/archives/2015/04/when-change-is-constant-a-spiral-ux-design-model.php

Ben Callahan's Responsive Process

from Smashing Book 5

Reference: https://www.smashingmagazine.com/2016/02/efficient-responsive-design-process/

nurun Human-Centered Design Process

Reference: http://www.nurun.com/en/what-we-do/

IDEO's Design Process

Reference: https://medium.com/digital-experience-design/how-to-apply-a-design-thinking-hcd-ux-or-any-creative-process-from-scratch-b8786efbf812#.42ul4ts9w

LitheSpeed's Design Thinking + Lean UX + Agile Process

Reference: http://lithespeed.com/lean-ux-dont-part-1-3-2/