map{/([^:]*?)(\s*\n|\s*:)/&&$1}@list;

# silly me ... distributive property! update: 34 chars:

map{/([^:]*?)\s*(\n|:)/&&$1}@list;


##</code><code>##

__DATA__
123 : oain:b:okfbd

456
foo bar    : df a dsaf asdf
111 :

##</code><code>##

map{(split/\s*(:|\n|$)/)[0]}@list;