StuffIt (formerly StuffIt Standard) is shareware and has been able to create encrypted Zip archives for many years. If Zip encryption is enabled, StuffIt uses AES 256. You can also optionally exclude Mac-specific content (ie: resource fork data and DS_Store files). With the 2009 release, you can make custom droplets, each with its own unique compression settings.
http://download.cnet.com/StuffIt/3000-2250_4-10151590.html