Here are some mods that I find rather nifty, but may not be widely known.
Does your roll window interfere with your casting or healing? Does it block important things on your UI? Well, move it.
Setup: Just move it where you want it, right click the frame to lock it, and you're good to go.
Wanna remember where your herb and ore nodes are so you can fly by later and see if it has respawned? Have your minimap track your node locations! Works for all node-specific gathering professions, as well as Hodir Ice Shards and treasure chests. Adds icons to your world map, and simple circle outlines when you get close to a node on your minimap so that any yellow tracking dots are visible.
Setup: works great out-of-the-box, though it does not come with pre-installed node locations. You can download locations with an additional addon, or hunt them out yourself.
For teh rogues! A moveable poison menu that will open/close at a click, listing all available poisons in your inventory and applying them to your MH with a left click, and your OH with a right click. Only useful for rogues.
Setup: just choose the position for your button menu.
We all know that if you can't learn a recipe, then it is colored red. Well, how about coloring the ones you already know with green? This mod will also color recipes that your alts already know, so that you don't buy a recipe for your alt only to find out later that it isn't needed!
Setup: works great out-of-the-box. Just make sure to open your professions tabs in-game for the mod to parse when you first install it.
Moveable paperdoll durability alert, PLUS it will add your durability percent to each item on your character equipment panel, along with an estimated cost of the repairs they require.
Setup: no configuration.
BA-DUMP! A working makeover of the old JIM'S CooldownPulse. Multiple frames are available with different scaling/opacity options, and you can choose to monitor more than just your spell cooldowns. Import any sound you wish to use as the pulse sound. Supports scrolling combat text alerts.
Setup: it works okay out of the box, but adding sound and personalization will take some work given the number of options available. Does not come with its own sound files. I recommend grabbing the lubdub.wav file from a JIM'S CooldownPulse folder and copying it to the GhostPulse sounds folder, then importing it in your in-game GhostPulse menu.
A purely audio mod that plays a sound each time you gain a combo point OR shaman maelstrom stacks, and when they reset to zero. There is an option to only play a sound when you reach the maximum stack of MW or CP, if you prefer. The defaults are subtle and non-distracting. You can add your own sound files to use, but personally, I find the defaults very nice.
Setup: works great out-of-the-box.
Do the skins on your action bars bore you? Make them cool and shiny with this mod! Simple skinning mod with additional presets available for download. The above skin is Entropy, one that I use. Gloss (highlight over the buttons) and no-gloss (just the border) options are available. It can also skin your Buffalo buff bars, if you use the icon format!
Setup: through the main WoW addons panel, it requires some selection of what mods you want to skin, and with what skin, and down to individual action bars if you wish. Additional skin designs must be downloaded and installed.