Solstheim Mage Tower V 3.0
Adds a mage tower and small settlement to the Alter of Thrond on Solstheim. While it is not the most spacious, it very atmospheric and provides the distinct feel of a rustic, isolated outpost, the type of place you'd expect to find in such a locale. It works very well in conjunction with the Pelegiad Archmage Tower because it provides quick transport from the Vivec Mage's Guild and the Archmage Tower mod does not (that I have seen) have a version that has been updated to Bloodmoon. There is also an optional side quest with the mod. A few relatively powerful items have been left in chests and closets (like glass armour), but by the time you hit Bloodmoon, this scarcely matters, and the goodies can be easily ignored.
Legionnaire's Signet Ring
This plugin is technically a cheat, but IMO it is more like an ease of use mod. It provides a couple of rings you can use when dealing with the Legion if you don't want to lug about their armour.
Cait's Donkeys and Horses Go Wild
Tired of all the reptilian lifeforms? This mod adds horses and donkeys all over Vardenfell
The work and detail is really beautiful. Warning, do not download if you are likely to experience significant framerate problems.
Waterfowl of MW Expanded
Adds *real* birds (ducks and geese) to Vardenfell, so that cliffracers are no longer the only lifeform with wings. As with the above horse mod, do not download if you are prone to slowdowns.