Recreating common Cocoa icons is a pain and wastes alot of time. Here’s a list of common icons people have released that can be used without restriction in your application:

• Add & Remove Icon : http://mabblog.com/blog/?p=133 —-There’s an earlier (and IMO better) variant of the plus/minus-icons here: http://boredzo.org/buttonicons —-
• Green Check & Red Cross Icons: http://mabblog.com/blog/?p=129
• RoyaltyFreeIcons by Matt Ball
• Add & Action (gear) Menu Icons: http://mabblog.com/blog/?p=135
• Other miscellaneous icons: http://scotlandsoftware.com/products/icons/
• Set of 32x32 iPod icons: http://www.jasperhauser.nl/icon/ipod_pack.zip
• The Tango icons are aimed at Linux Desktops but look good in Cocoa Apps too: http://tango.freedesktop.org/Tango_Icon_Gallery