I love interesting foliage. Leaves are there all the time, not temporary at all like flowers are. I can enjoy them any time of the year. The fact that my plants never re-flower might be part of that but... anyway, have some cool foliage!
It seems like all the cool trees come from Australia. Banksia grandis gets from 16' to 32' in height and Annie's Annual's puts this at Zones 9 - 11. The foliage is pretty darn neat, just a bunch of triangles hanging from branches, giving it a saw-toothed sort of look. And what are those pinecone things on it? The lighter ones are bundles of flowers which reach 12" in length. The darker toned ones with those odd "duckbills" on them are the seedpods and the duck bills are where the seeds pop out. The seed pods are pretty woody and are sometimes sculpted into vases or other nifty things (as seen above).
This tree is also from Australia. I suppose it's a confier but its pines are very different from any run-of-the-mill pine tree! Wikipedia says it can grow anywhere from 98' to 147' which is pretty impressive. Its pine cones are just huge enough to match it! Dave's Garden puts A. bidwillii at Zones 8b - 11, making it only just slightly more accessible for growers around the world. Because of its immense height, I don't know anyone who would grow it indoors without some major pruning....
A member of the same genus as our previous conifier, Araucaria araucana is next. Most commonly known as a the monkey puzzle or monkey tail tree, it grows in Chile, Argentina, and Brazil naturally and can reach heights of about 130' tall with a 7' trunk diameter. It's Zones are listed on DG as 7b - 10b and Wikipedia seems to praise it for its hardiness in comparison to the rest of the genus. Interestingly enough, its seeds are a food crop in Chile and have the potential to be a major one in other areas. Mature trees can produce several thousand nuts in a year but it takes 30-40 years for trees to mature... I think it would be worth planting a small orchard for definitely. Maybe the nuts could be the next acai berry or goji berry, haha. If you do want nuts though, it would be best to get more than one tree seeing as A. araucana is usually dioecious. I know I will definitely plant a couple... as long as their branches don't try to land on me. I swear, those leaves look like shuriken!
This handsome fellow is native to New Zealand and DG puts it in Zones 8b - 10a. As a juvenile the tree will look much like the bottom most picture. Leaves up to about 15" line most of the tree and are wonderfully toothy and dark in color. The tree takes about 10 to 15 years to mature and once it does the leaves become shorter, wider, and more green in color. So, while some plants take years to be cool, this one is coolest at a young age and gradually becomes less extreme as it ages. Don't get me wrong, the mature trees look great, just not as neat.
Oh look, something that's not a tree! A cactus from southern Mexico, S. anthonyanus is an epiphyte. Seems to do pretty well in hanging baskets, blooms are night, and is easy to propagate and grow in general. DG puts it at Zones 10a - 11, so definitely something to keep inside! It's common names are Ric Rac (Orchid) Cactus and Fishbone Cactus. Flowers range in colors but most seem to be like the one pictured or yellow. Requires moist soil high in organic matter but I'm sure drainage is still important. Full sun or part shade should be fine. (I really really want this one! So cool!)
Commonly called Butterfly Leaf or Swallow Tail, DG puts it at Zone 11 only. Reviews on DG seem to indicate that it's a bit finicky and hard to grow but it sounds like as long as you keep it pretty wet and feed it regularly it'll be fine. An interesting tender perennial that looks like it'd be cute in a pot, I'd definitely grab it if I saw it, if only to give it a go.
Dyckia fosteriana in bloom
Dyckia... no matter what the species, these Brazilian/South American bromeliads come in all kinds of interesting shapes, colors, and sizes. Their leaves are thick and spiny, the plant clumps, it's supposedly the hardiest kind of bromeliad (prefering 40-90F and easily withstanding lower temps), it's primitive, and finding any for sale is lucky. I've yet to see any personally, but oh my god, I think I'm in love. New species are still being found... I wish I was a part of that! But no, I haven't even started college for botany yet. Oh well, hopefully there will still be plants out there for me to discover! Great sources to learn more about Dyckia include: the Dyckia Brazil blog and this Bromeliad Society/Houston page.
There are so many more plants I can think of that have interesting foliage but...this post is long enough haha.