Magazines: Layers magazine http://www.layersmagazine.com (for all Adobe products)
Professional societies: National Association of Photoshop Professionals (NAPP) http://www.photoshopuser.com $99/yr gets full access to Web site (including tips/hints), discounts on training (online and DVD-based), and subscription to Photoshop User (available only to members)
Tips, tricks, training: http://www.photoshoptraining.com , http://www.lightroomkillertips.com , http://www.photoshopkillertips.com , http://www.photoshopcafe.com
Podcasts: Photoshop User TV (subscribe via iTunes or view/download at http://www.photoshopusertv.com)
For those interested in designing for print, can't say enough good about Before & After (http://www.bamagazine.com). Available both in print & as PDF. Great advice about both print & Web design.
