I've grown fond of the JavaScript || idiom:

 function FrobImage(img) {
     var width  = img.width  || 400;
     var height = img.height || 300;
     // ...
 }

 FrobImage({height: 100, name: "example.png"});

If img.width exists and it's truthy, then width = img.width; otherwise, width = 400. Here, it will be 400 since the img hash has no width property. More than two alternatives may be used: x = a || b || c || ... || q;

A few weeks ago, while cleaning up the error handling in some batch files, I came across a similar idiom:

 foo.exe bar 123 "some stuff"  || goto :Error

Only if foo.exe fails (exit() returns a non-zero value), is the second clause executed.

Perl's die is typically used in a very similar idom:

 chdir '/usr/spool/news' || die "Can't cd to spool: $!\n"

though the or keyword seems to be preferred nowadays to ||.

This morning, I came across the ?? operator in C# 2.0, aka the null coalescing operator:

 Customer cust = getCustomer(id) ?? new Customer();

If getCustomer(id) is not null, then that's the value that cust gets; otherwise it's set to new Customer().

All of these idioms are syntactic sugar and all of them are in my toolbox.