Photoshop is hands down the best photo editing and manipulation software on the market. GIMP does a good job of not sucking, but it still doesn't really come close. Search "thethingy" torrents for anything adobe you wish, dude's been wrecking their software for years.
BTW, I see a lot of illustrator recommendations. It is definitely one of the best softwares for creating designs and vector artwork... but I'd recommend CorelDraw over it. Especially with a few of the right tutorials, bezier tool with viewable nodes... CorelDraw easily compares with Illustrator and is more effective/easier to learn for many tasks. Illustrator still has some things it does better than CorelDraw, don't get me wrong. But it's way overrated, mainly just because 95% of graphic design courses push Illustrator.