Some that didn't make the list are:
10. Sayid and Nadia
Even though he had a relationship with Shannon, I think Sayid's heart always belonged to Nadia. They were childhood friends and then met again as adults when Sayid was forced to torture her for information, but ended up letting her go (Ep: 1x9, Solitary).
When Sayid got off the island he spent a lot of time with Nadia, but she was killed when she was hit by a car (Ep: 5x16, The Incident).
9. Hurley and Libby
Hurley and Libby met on the island when the tail section survivors met up with the fuselage survivors, though she was at Santa Rosa Mental Institution with him and could have met him there. If they did meet there, he doesn't remember.
8. Daniel and Charlotte
Daniel and Charlotte weren't technically a couple, but I was moved by how deeply they cared about each other. As far as we know, they met when they were hired to go to the island, although, Daniel did visit Charlotte when she was a little girl.
Daniel stayed with Charlotte as she died due to the effects of jumping through time.
6. Jack and Kate
Jack and Kate met on the island when she stitched up his back. They became very close, though had an on-again-off-again relationship as Kate also had feelings for Sawyer and Jack got close to Juliet.
The two had a relationship after getting off the island, but it fell apart.
5. Jin and Sun
We've seen this relationship through a lot. First we saw Jin as an overbearing husband and Sun as a meek housewife. As time went on, though, we realized that Sun is a very strong woman and Jin was head-over-heels in love with her when they first met.
Sun and Jin met when they bumped into each other and Sun dropped her stuff. Sun didn't believe she would be allowed to marry Jin because her family was very well off and he was the son of a fisherman. They did get married, however, and Jin worked for Sun's father.
By the time they crashed on the island, they had grown apart, but grew close on the island.
4. Charlie and Claire
3. Rose and Bernard
2. Desmond and Penny
Desmond met Penny when he was kicked out of the monastery. She was picking up wine for her father and he ended up going with her to deliver it (Ep: 3x17, Catch 22).
Penny's father, Charles Widmore, did everything he could to keep Desmond away from Penny, but they reunited when Penny's boat found Desmond and the Oceanic 6 floating in the ocean after their helicopter crashed (Ep: 4x13, There's No Place Like Home Part 2).
1. Juliet and Sawyer
They were tossed around in time, and when it was time to leave on the sub in Dharma 1974 times, Sawyer asked Juliet to stay. Their love grew during the three years they lived with Dharma and Sawyer was going to ask Juliet to marry him (Ep: 6x3, What Kate Does).
In the end, the electromagnetic force was released, and Juliet was pulled into the Swan hole after Sawyer tried to save her (Ep: 5x16, The Incident). She detonated the bomb and ended up under the imploded hatch rubble in 2007. Sawyer climbed down to her and she died in his arms (Ep: 6x1, LA X).