One good investment for your wardrobe is a cardigan. Use it as substitute for the suit jacket in the office, or casual with jeans. It also works great for a dinner out with a skirt or dress, especially if you live in cold places like myself...
These are some of my favourites right now:

On picture from left: Black cardigan from By Malene Birger (www.net-a-porter.com), light grey cardigan from Sonia by Sonia Rykiel (www.mrsh.se), jeweled cardigan from Tory Burch (www.net-a-porter.com) and wool sweater from Moschino (www.net-a-porter.com)