Wood is always the best way to go. It never goes out of style and always looks elegant yet simple and is easy to keep neat and clean. If you have a certain color scheme, try to find anything that color and add it to your decor. Each colorful piece will add to the decor nicely. White or ivory is always a good choice, it looks neat and clean.
Blues never goe out of style and gray is a new popular color in all shades from charcoal to silver.
If you must spend some money, spend it redoing floors, especially wood floors. Get a new leather piece or have bookshelves or an entertainment center built in. New, updated countertops will transform you kitchen. Get a new dining table. The ones with the iron legs or accents are beautiful.