There are a huge host of options. From the Adobe suite of products, Photoshop included, to many freeware options, GIMP for instance. The problem is, the software itself doesn't impart any artistic advantage and beyond that the software often requires a considerable amount of time to master. If you have an idea in your head, I suggest you write and sketch it out as best you can and post it here, I'm sure many people would be happy to help in bringing your ideas to life - myself included. Best of luck!