Maya 2015 with Nightshade UV Editor - https://www.creativecrash.com/maya/script/nightshade-uv-editor
Vasty extendes the UV editing options avilable over the base UV editor of Maya.
Quixel Suite 2.0 - http://quixel.se/
An awesome alternative workflow for texturing models and outputs for all frequently used software packages and game engines. includes nDO which is great for creating normal maps in photoshop from textures, or from scratch for detailing a model.
Substance Player - https://www.allegorithmic.com/download
I use this in combination with the plugin from gametextures.com (https://www.gametextures.com/gametextures-to-metalness-a-new-tool-to-convert-workflows/) to convert between texturing workflows and outputting to PBR.
AMP Tile Viewer - http://www.ampsoft.net/utilities/TileViewer.php
useful tool for veiwing tiled textures
xNormal - http://www.xnormal.net
for baking normal and ambient occlusion
CrazyBump - http://www.crazybump.com/
good for displacement maps and as an alternative for creating normal maps from
Other useful tools
SageThumbs 18.104.22.168 - https://code.google.com/p/sagethumbs/
good for viewing thumbnails not supported by default in Windows (such as .tga and .dds)