36 chars and handles blank lines, empty lines and lines starting with a colon: 
@list = (
  "123 : oain:b:okfbd",
  "",
  "456",
  "foo bar    : df a dsaf asdf",
  "111 :",
  ":  adf",
  "      "
);

$, = "\n";

print map{/(.*?)(\s*:|\s*$)/;$1||()}@list;

[download]
Chokes if the values in front of the colon is '0'.

Update: 33 chars (destructive): 

map{s/\s*:.*|\s*$//;$_||()}@list;

[download]
Update: 32 chars (destructive): 
map{s/\s*(:.*|$)//;$_||()}@list;

[download]

In reply to Re: golf anyone? (taking first field) by busunsl
in thread golf anyone? (taking first field) by John M. Dlugosz

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