like a mauler? theres not many quests that will get you ONLY strength. they either give additional exp for other skills, or the requirements include other combat skills.
if you want to get some attack as well, then waterfall, tree gnome village, gnome stronghold, the grand tree, MM and all that. have a look here though, very helpful :*)
http://runescape.wikia.com/wiki/Quest_experience_rewards
Strength quests:
* 100 - The Blood Pact
* 600 - In Search of the Myreque
* 2,000 - In Aid of the Myreque
* 2,500 - Tai Bwo Wannai Trio
* 2,812 - The Fremennik Trials
* 3,000 - Land of the Goblins
* 3,075 - Heroes Quest
* 4,000 - Troll Romance
* 4,662.5 - Horror from the Deep
* 5,000 - TokTz-Ket-Dill
* 6,625 - Scorpion Catcher
* 9,000 - The Curse Of Arrav
* 10,000 - Roving Elves
* 13,750 - Waterfall Quest
* 18,650 - Dragon Slayer
* 20,000 - The Chosen Commander
* 20,000 or 35,000 (optional when you speak to Daero) - Monkey Madness
* 22,000 - Haunted Mine
* 30,000 - The Path of Glouphrie
* 30,000 - Forgiveness of a Chaos Dwarf