If you haven't finished your holiday shopping yet—first of all, it is OK. Neither have I. Secondly, here are a few more ideas for the gardeners on your list:
I suggest a gift certificate to a local garden center, or to a fantastic mail-order nursery. The rest of the winter can be spent dreaming how to spend it. If that seems too impersonal, how about the Pewter Glass Display Boxes from H. Potter? I think they are gorgeous, especially for showcasing an orchid or miniature African violets.
I also like their trellises, especially the Love Knots trellis.
Lastly I would recommend—for the giver short on cash or for the recipient who has everything—the sincere promise of help with a garden chore or project in 2012. Be specific, and follow through! Giving this on a note with one of Horticulture's 2012 calendars would be cute. The wall calendar has lots of gardening tips for every month; the desk calendar has a space-saving design and a nice monthly garden image.
Horticulture's community leader, Patty Craft, recommends Lechuza self-watering containers, which she loves using for her patio's container garden.
Patty also likes the Perfect Choice Furniture 2-Person Glider, which has the comfortable styling of an Adirondack chair but seats two. It is made in the USA.
Jenny also points out we're not all lucky enough to have our own greenhouse, so a great midwinter gift for gardeners are indoor grow lights, for seed starting or flowering houseplants. She likes the table-top Jump Start system from Home Harvest Supply.
Browse hundreds of great gifts, from books to tools to design items, at GardenersHub.com.