Depends if you are looking for lore-friendly mods, or just some fun ones. One mod I always apply however is the Immersive Saturation Boost by Aplestormy. This is a must if you prefer the brighter, more colorful graphics of Oblivion, or are just tired of the same old gray textures.
http://steamcommunity.com/sharedfiles/filedetails/?id=128490856&searchtext=saturation+boost
*This will take you to the Steam workshop page for the mod.
If you are looking for arguably the best companion mod on the market, then you definitely have to check out Inigo by Smartbluecat. Not only does he have thousands of lines of custom dialog, he has also been professionally programmed to add custom mechanics such as moving out of your way when you are trying to walk through a doorway, or being able to pick up loot you miss while dungeon crawling.
http://www.nexusmods.com/skyrim/mods/40960/?
*I included the nexus version of the mod as the Steam workshop version is no longer being updated.
If you can give us a little bit more information about what you are looking for, I'm sure we can recommend some more mods. These were just a couple that I believe most people will enjoy.
Welcome to the wonderful world of adding mods... and never playing... no...just kidding.. maybe..
http://www.nexusmods.com/skyrim/mods/3829/?.. exactly what it says...
http://www.nexusmods.com/skyrim/mods/24913/?... their is a "lore" friendly version, but I like the original just fine.
http://www.nexusmods.com/skyrim/mods/searchresults/?quicksrc_name=File+name&quicksrc_auth=arthmoor&quicksrc_game=110... They are all good...
http://www.nexusmods.com/skyrim/mods/34492/? add's new places to the Northern parts of Skyrim.
Their are many many mod's I could add... I have 58 pages of "tracked" mods...354 downloaded... not all are compatible and I don't use even half of those together, but the majority are clothing/ armor... texture, envirornment and other things along that line.