This is one of the better places to download mods and plugins, and
this is where i got most of my mods from, but for some reason the page wouldn't load for me anymore. The first one is still good though, and they probably have the same stuff as the second. How to install mods and plugins is all described on the sites, and is easy to do.
Of course you also have to visit Bethesda's site for a few official plugins, if you're interrested that is.
I got a few that make your life a little easier in Vvardenfell, such as a few houses for my character. I got the "Balmora residence" plugin, and the "Vivec residence" plugin, since i spent most of the game roaming those cities anyway. But there's a residence plug for almost every city or little town in the game, so suit yourself.
I also got the "Giants mod" which makes the game a little tougher. There are some new monsters added, such as Seadevils, and Ancient liches (which can be very tough to beat), and Nixhounds now hunt in packs, and come at you with 6 or 7 all at once. And of course there's giants roaming the wilderness now, who attack you on sight. They're huge halfnaked barbarian type of creatures, who carry weapons too heavy for you to carry. I once killed one, and tried to pick up his axe, but it weighed 1000 lbs. So never mind.
I also got the official Bethesda fletchershop plug, which adds a fletchershop where you can buy all sorts of ammo for your bow in the Vivec foreign quarter waistworks.
The "Creeper trader" plug is something to bypass all those low cash merchants in the game. The Creeper, who normally has 5000 to spend every 24 hours, now has 100.000 every 24 hours, so now i can sell all that glass and daedric stuff as well.
I also have the "armour mannequin" plug, which allows you to buy wooden mannequins to place in your residences, which you can fully dress with all the armour you find in this world. Looks pretty cool.
see for yourself
But there's so many more out there, just check the link, and see if there's anything you like.