I don't know about others, But I use the Shouts Aura Whisper and Slow Time very frequently. Aura whisper is insanely effective in scouting out enemies before entering into combat and is very efficient because you don't have to use your mana reserves to cast a 'detect' spell. With the perk that silences your spellcasting (it also affects your Thu'um), Aura Whisper is always my opening spell before entering a fight (I usually play a stealth based character, so prior recon is very important.)
Slow Time is another beast entirely. Big bad boss? Your health too low for your liking? Pop in the Slow Time and hack away!! I use it most frequently to dodge those nasty fireballs when fighting pesky wizards and dangerous Hagravens. If you can time it right, it is almost always a game-changer, capable of turning the tides of a battle in an instant.
Now, if you are a more combat oriented, burn-them-all kind of person, then you should definitely consider the fire breath shout. With insanely high damage and massive utility (with meditating the 'Fire Within' from Paarthurnax and if you have Dragonborn DLC installed, 'Dragonborn Flame' ability that summons fire wyrms for each enemy killed with the Shout), it is a must-have Shout in your repertoire and is the One-Shot-Solution for those groups of critters that dare interrupt hoarding burnt books while on a nice little stroll in that dungeon.