I love Internet shopping for plants (and just about anything else) because the variety is vastly greater than what is typically available locally. Generally, neighborhood nurseries try to keep a wide selection to appeal to as many people as possible, but if you want something special, you likely need to to shop via mail order.
There are all sorts of online shops specializing in all sorts of plants. But to get you started, Etsy has a growing selection of interesting suppliers, and I thought I would share with you some of my favorites.
1. Succulent Beauties. There are so many different kids of succulents — you could get lost in this one plant genus alone. Most nurseries around here have perhaps 10 varieties — this Etsy shop has hundreds. And if you want to learn more about them, I highly recommend Debra Lee Baldwin's Succulents Simplified: Growing, Designing and Crafting with 100 Easy Care Varieties.
2. Tillandsias are very trendy plants at the moment, probably because they are easy to care for, and because they are ephiphytes and don't need soil, which means they can be used like a decoration to grow on most anything in your home. Epiphytes are plants that grow on other plants or objects in a non-parasitic way. They derive moisture and nutrients from the air, rain, and sometimes from nearby debris that might accumulate on them. CTS Airplants has a huge selection of these plants.
3. Mr Nature is my kind of Etsy shop. The eclectic selection is clearly curated by a plant nut who likes plants that have a purpose (i.e. there is some sort of fun crop to be had) or are just plan fascinating. None of them are things that you can readily find elsewhere. I have my eye on some Apple Gourd Seeds for next year.
4. Maya Garden Inc. is a Bamboo specialist. These unique plants are fun to plant in containers, and the canes have all sorts of alternate uses at the end of the season.
5. And if you are looking for more traditional tropical plants (most house plants fall into the category of tropicals), check out US Tropical Plants for a great selection. These White Caladiums caught my eye, as the holiday season is coming soon.