What size should an application icon and menu bar icon for OS X be?
I can deal with small resolution displays but what about Retina - does an icon displayed on the men
Follow these steps and you will get a perfectly sharp status bar Icon for retina
The maximum size for the app icon should be 1024 x 1024.
And you have to create both regular and retina resolution icons for 16 x 16, 32 x 32, 128 x 128, 256 x 256, 512 x 512 & 1024 x 1024.
The details for which you can find in the "High Resolution Guidelines for OS X" document from Apple.
adding on to Michael's answer apple are now requiring all the way up to 1024x1024px icons due to retina displays.
http://www.cultofmac.com/179738/apple-now-requires-high-res-1024x1024-icons-for-every-mac-os-x-app/
To make your menu item support Retina displays, Dark Mode and different states (e.g. pressed)
NSImage(named: "Example")
NSStatusBar icons (i.e. Menu bar icons) are different from regular app icons. I have not been able to find an NSStatusBar official icon guideline, but I have to believe that the Toolbar Icon guideline for buttons is pretty close. It suggests:
In testing, I've found:
Code sample:
myStatusItem = [[NSStatusBar systemStatusBar]statusItemWithLength:NSSquareStatusItemLength];
NSImage *statusImage = [NSImage imageNamed:@"Status.png"];
[myStatusItem setImage:statusImage];
NSImage *altStatusImage = [NSImage imageNamed:@"StatusHighlighted"];
[myStatusItem setAlternateImage:altStatusImage];
[myStatusItem setHighlightMode:YES];
[myStatusItem setMenu:self.myStatusMenu];
http://developer.apple.com/library/mac/#documentation/userexperience/conceptual/applehiguidelines/Intro/Intro.html#//apple_ref/doc/uid/TP30000894-TP6
And: http://developer.apple.com/library/mac/#documentation/userexperience/conceptual/applehiguidelines/IconsImages/IconsImages.html