edit: And I'd like to second the recommendation of http://tesnexus.com/downloads/file.php?id=15697 from earlier in this thread.
I've enjoyed the http://planetelderscrolls.gamespy.com/View.php?view=oblivionmods.detail&id=4451 mod by Colt17. It makes the different kinds of potions different colors, making them easier to find at a glance, especially if you use a grid system inventory.
I'm a big fan of http://planetelderscrolls.gamespy.com/View.php?view=oblivionmods.detail&id=4729. It adds 16 more hotkeys and it brings up the same kind of visual interface for them that the 8 original hotkeys have.
http://planetelderscrolls.gamespy.com/View.php?view=oblivionmods.detail&id=1037 is another favorite, adds a bunch of new sigil stones for you to find, some of which are actually worth using!
I also never play without http://planetelderscrolls.gamespy.com/View.php?view=oblivionmods.detail&id=360 by daleth. I don't know if it counts as "little-known" as it has over 6,000 downloads, but it's still a really nice mod. I like being able to fast travel to way shrines and doom stones - there are less monsters hanging out there that want to eat my horse.
http://tesnexus.com/downloads/file.php?id=22326 also "adds 16 more hotkeys and it brings up the same kind of visual interface for them that the 8 original hotkeys have", but does a bunch more. Admittedly it's a bit buggy in places, and is too popular to qualify as a "little-known gem", but you might want to add a reason that doesn't also apply to a more popular competitor. (full disclosure: I wrote Super Hotkeys)
Likewise, http://www.tesnexus.com/downloads/file.php?id=7341, based upon the mod you linked, is more popular (by download count anyway) and more recent (and is available from tesnexus, which I have an easier time with than PES). Why that one?