Here are a few examples ...
Graphics ToolsNot everyone can afford professional software applications unless it's part of their daily work. In many cases I find online photo editors can be just as useful, especially if you're only re-sizing or cropping an image before uploading it to your digital signage app.
I have found EDITOR by Pixlr and Photoshop Express Online Apps which are great for quick image edits. Note that Adobe is phasing out their Photoshop image storage plans in favor of a new service called Adobe Revel but you can still use the Photoshop Express Apps to edit your images and store them on your local PC.
I also use online web design resources for some of my digital signage content work. Sites like Subtle Patterns or Patternizer are a great place to start when designing a template background or other visual element.
Colourlovers is another great source of inspiration for anything related to colours. It's easy to get lost on this site but it's worth a visit if you want to discover new colour palettes or are simply looking for new ideas to incorporate into your next digital signage project.
Video ToolsIf you are an Adobe After Effects user, you must check out this blog article. It lists 28 best motion graphics blogs and resources. It's a bit technical for novices but still offers a lot of neat information and inspiration.
A lot of digital signage pros use After Effects so it's worth checking out if you are serious about your content.
I also found an online video bitrate calculator. It's quite technical but worth a read if you want to learn more about video file optimization.
photo credit: Aristocrats-hat via photopin cc