Are you shooting JPG or RAW?
You have multitudes of programs to get your photos from your camera and into a spot where you can start editing/sharing/etc.
- iPhoto. Great if you're not planning on editing a lot of photos. Slow and really not well optimized for a RAW workflow. All your files are stored in the iPhoto Library.
- Image Capture. This program will allow you to download and save the files wherever you want and allows you to manage your photos however you want. The files are visible right within Mac OS X since the OS itself has support for many RAW formats (including your 5D and the 5D Mk. II if that's what you have)
- Finder. You can open up your Compact Flash card (either via a card reader or via the camera acting as a card reader) and simply drag and drop your photos and then edit them with whatever program (eg. Photoshop) you want.
- Aperture is Apple's RAW workflow/photo management application and allows you to take RAW files from the 5D store them in it's library and then edit your pictures within the application. Most of the edits on non-destructive as well. You're able to edit these photos in Photoshop or other image editor (eg. Acorn, Pixelmator) as well and the resulting edited file (a .tiff) will be added to your library. It does work with JPGs as well if you start off by shooting JPGs.
- Lightroom is Adobe's RAW workflow/photo management application. Personally it's my favourite as it has nearly all of the features that Aperture does plus more. It does with JPGs as well.