Studies have shown that having flowers in the home has an immediate, positive impact on mood. Yes, they're temporary (a flowering plant is a nice alternative), but they have a longer-term impact on mood and depression. And who doesn't like the warm surprise of opening the door and seeing flowers there?
http://www.associatedcontent.com/art...od.html?cat=51
Most florists stock chocolates or other gourmet edibles if you wanted to tack something on of that nature (they won't melt during delivery from a local florist to your friend), and the florist can take your card message over the phone.
Something to consider, in any case.