The best place to start in predicting the Grammy nominees for Song of the Year is the likely Record of the Year candidates. (Record of the Year honors a particular recording of a song. Song of the Year, which is awarded to the songwriter, honors the song itself.)
This year, three likely Record of the Year finalists are also eligible for Song of the Year. They are Carly Rae Jepsen's smash "Call Me Maybe" (which she co-wrote with Tavish Crowe and Josh Ramsay), Frank Ocean's "Thinking Bout You" (which he co-wrote with Shea Taylor) and Mumford & Sons' "I Will Wait" (which the four band members co-wrote). Mumford & Sons was nominated for Song of the Year last year for "The Cave."
Two other likely Record of the Year finalists—Adele's "Set Fire To The Rain" and "Somebody That I Used To Know" by Gotye featuring Kimbra—inexplicably weren't entered for Song of the Year. That leaves two slots to be filled. There's no shortage of songs to fill them. A whopping 778 songs are on this year's eligibility list, though only a couple of dozen have a real chance of being nominated. The nominations in the top four categories are determined by a panel of Grammy insiders.