http://www.gamespot.com/snes/rpg/legendofzeldaalinkttp/show_msgs.php?pid=588436&topic_id=m-1-57595591
I was wondering about this myself and found this thread a while ago. What AmazingAmpharos says seems to be the most correct. Swift_Strider's list is correct except that 6 can be before 2 because of what AmazingAmpharos says about crossing the gap in the first room of 6. I can confirm this as I have done 1,4,6,3,2,5,7 myself following this advice.
For those of you who don't want to follow the link:
AmazingAmpharos says "In terms of Dark World Dungeons...
1 obviously requires nothing.
2 requires the Hammer to get in and Flippers once inside.
3 requires the Hammer to reach.
4 requires the Hammer to reach.
5 requires the Titan's Mitt to reach and either the Fire Rod or Bombos to complete (Fire Rod heavily advised). There's a room that is possible but not "normal" to avoid that can get you stuck if you don't have the Hookshot (which is also incredibly useful for combat in this dungeon). The Cane of Somaria can be used to save a ridiculous amount of time in this dungeon but is obviously not required.
6 requires the Titan's Mitt (and Flute) to reach but no other treasures once inside. You can cross the first room with the Pegasus Boots dash bashing the blocks; you don't need the Hookshot like it seems.
7 requires the Titan's Mitt and Hammer to enter, the Cane of Somaria to transverse, and the Fire Rod and Ice Rod to clear the boss.
I left out required items that you would be sure to get just playing through the Light World.
The most efficient general dungeon order is this:
1, 4, 2/3/6 *(order is largley preference), 5, 7"
Swift_Strider says "- #1 is obviously first for the hammer
- From there you can skip 2 and go to either 3 or 4. Most prefer 4 first for the mitts that give you access to your lvl 3 sword.
- You can do 6 anytime after you finish 2, and 5 once you've completed 2 and 4.
- 7 can be done anytime after you complete 3, 4, and 6." Note once again that 6 can be before 2 which is the only mistake I can find.