Bookends  

Jacks..
I have some cast iron Jacks I use as bookends, that double as a door stopper. Like these 😀

I
use clear perspex (lucite) L shaped bookends
They are virtually invisible, and unobtrusive

I've seen yours on ebay...
I've seen yours on ebay before - very nice!
Seen apart from the invissible ones I have this ancient marble piece (an eclectic addition to the interior):

These are readily ...
These are readily available by Chris Collicott.

Clever!
Clever!

Although I'm not crazy about their furniture,
you can't beat IKEA for nifty, well designed and cheap bookends.

barrympls, IKEA, brilliant, I...
barrympls, IKEA, brilliant, I always overlook them I'm sure for the same reasons that you don't like their furniture but, they have a very simple stainless steel 1 for $2.99. How can you go wrong with that?

L-shaped lucite, too--
almost invisible, perfect for cantilevered shelves.

.
I use rocks.

ben seibel rocks
i do like the simplicity and economy of woodywood's solution; it's tough to top nature.
nonetheless, ben seibel did a line of slide stoppers for raymor in [i'm guessing cast iron heavily plated in] copper and/or brass.
resale of these babies seems to me quite steep, especially considering they function about the same as the aforementioned litho method, with the addition of a nifty green felt pad, of course. but they do look pretty cool.
here are a few samples to get started [i hope these links work ... i've not done this in a while]:

Decorative bookends would drive me crazy
I know I'd end up compulsively arranging the books on the end of the stack to best compliment the sculptural bookend, and that's not a rational way to organize books.
And, nothing works quite as well as the classic L-shaped design.

two more
I just got some shelving that requires bookends. I got these Danish-made teak bookends at an auction. The weird thing is that they're candleholders! Who puts lit candles next to books?! I have them on a high enough shelf that the candle holes are not visible. And I cleaned all the wax drips off. They were reminiscent of Chianti bottles in a cheap Italian restaurant in 1967.
The second pair are also from an auction (I paid $2 per pair--woohoo!). Nice, simple cast aluminum. I was thrilled to get them.

The L shape
is the most common, but wouldn't a "T" work best? The "L" tends to slip when you take out a large book. I would think the "T" with a rubber bottom would grip the best.

"Who puts lit candles next to books?"
The Danes are reckless pyromaniacs capable of putting lit candles ANYWHERE.