There's 'The Sand and the Leaf's Union'. This fanfic focuses on the political implications of their marriage. It shows how the two ninja villages, Suna and Konoha, start to collaborate more closely as a result of Gaara and Naruto's relationship. The story also has some really sweet moments between the two characters, like when they go on secret dates in the forest between the two villages.
I've read 'Naruto and Gaara: A New Chapter'. In this one, Naruto is the one who first realizes his feelings for Gaara. He starts to send little gifts to Gaara secretly. Gaara, initially confused, soon realizes what Naruto is doing. The story then delves into how they deal with the reactions of their friends, like Shikamaru and Kankuro, who are a bit shocked at first but then come to support them.