I've been using my MacBook Pro since a while now and I must say: I really love it. The most common app(s) that designers use has to be Adobe Photoshop (Or the full suite). The app(s) are great, but there is a downside: The price tag. Photoshop CS4 costs $699, CS4 extended is $999 and the full Creative Suite starts at an stunning $1799. For many people this is just a little bit too much to "play around with".
Luckily, there are also many free applications out there that can do the same kind of job that Photoshop could do for you. This article rounds up the best 15 free Mac Programs for Graphic Designers. Some of these applications can even do stuff that can't be achieved using Photoshop, or are much more simple to use.
The most popular of all free photo editing software, GIMP stands for GNU Image Manipulation Program, and is highly-supported and frequently updated. Comparative to Photoshop, users can perform basic tasks such as photo retouching, color correction, and image size, or more complicated tasks like image composition and creation. GIMP has a scripting interface for advance users, as well as plugins, extensions, and filters.
If you want GIMP, but don't have X11, then Seashore is the appropriate software for you. Based on GIMP, it has nearly all the settings and functions of the more advanced program without the higher requirements.
An excellent alternative to Adobe Illustrator and CorelDraw, Inkscape is a free vector graphics program supporting standard SVG format, as well as XML and CSS standards. This program can do everything you'll need in a vector graphics program - tracing, path operations, direct XML editing, etc. Import and export formats include all the common image types, including JPEG, PNG, and TIFF.
Front End Digital Media Workshop
Don't waste time manually resizing individual photos for your various projects. Front End Digital Media is a batch conversion app for images (as well as video and audio), and allows you to mass resize, resample, split, join, and up/down sample JPEG, PNG, TIFF, BMP, PSD, and PICT image files.
The biggest appeal for the Image Tricks app is the ability to apply dozens of different filters to over 20 different image formats. The finished photos can then be exported as either TIFF, JPEG, or PNG.