Another alternative:

if ($condition) { 
   do_something(); 
}
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A couple of things:

1. I've found that the braceless if can slow me down when reading C code. I have to remember that the next command is the thing that's done.
2. Cuddling the braces around their control statements saves a lot of whitespace without much loss of readability. Consider the following extension of my suggestion above:

if ($condition) {
   do_something();
} else {
   if ($another_condition) {
      do_something_else();
   } else {
      do_yet_a_third_thing();
   }
}
[download]

Just my $0.02