We will start from the obvious to the more obscure. My design toolkit is ever evolving, but right now I rely on a few tools pretty much every single day.
Standard $99 / Pro $199
The backbone of my design process begins with wireframing in Omnigraffle. There are equivalents out there for it like Balsamiq or Axure that will also do very similar things. However, I use Omnigraffle. It is a great software with many free and paid stencil kits out there to jump start the wireframing process. My three go-to-stencils are Konigi Wireframing kit, the latest Twitter Bootstrap kit, and the latest iOS kit. Best part, they’re all free. Omnigraffle is great for getting layouts done quickly and cleanly for your client. It is vector based so you can stretch and manipulate all the stencils to your heart's desire.
Konigi Wireframing Kit (free)
iOS7 Wireframing Kit (free)
Plans from $19.99 per month
You know the drill. Photoshop, Illustrator, and InDesign are the three big dogs. There are a bunch of other great pieces of software as well, but I mostly use these three. I use photoshop for graphics and mockups, illustrator for making a lot of elements and working on logos, and inDesign I use for type based print projects. I will be discussing photoshop lightly here today. Photoshop is great for doing mockups and making graphics. I feel the most comfortable in this software to do fine detail work. I wish I could combine the powers of Photoshop, Illustrator, and InDesign together and I really hope Adobe does that some day. How awesome would it be to have the type options of InDesign, the vector powers of Illustrator (PS is getting way better at this FYI), and the graphic manipulation powers of photoshop all in one? It would be phenomenol. Anyway, I digress. There are a few extensions for Photoshop that will help you out and make your work flow more succesful
GuideGuide is a great extension tool to quickly add guides to very specific points on your canvas. You can also save presets and use them whenever you like. Now you know everything is lined up exactly where it needs to be.
Adobe Kuler (free)
This is a great extension for creating the start of a colour scheme. There are a lot of presets to sift through, but you will have to be patient to find a good one. Really, its great for getting a colour scheme started. Once you have an idea use this technique from graphic design Erica Schoonmaker. It is based off old ink and paint mixing techniques.
Creating Harmonious Colour Schemes (really helpful, check it out!)
Actions are pretty amazing. You can record what you are doing so you can automate the process the next time. Window > Actions > Create New Action. This places you automatically into record mode. You then see a red dot signifying record. Everything you do now will be recorded. Once you've hit stop you can play this action back and it will do everything you just did almost instantly. You can also download other people's actions. There are some great photo treatment actions that allow you to instantly achieve that Instagram look.
Check out Blogspoon Graphics for some good actions: Instagram Actions (free)