I feel like there are some "essential" riffs that every beginning guitarist needs to know (i.e., Sunshine of Your Love, Smoke on the Water, etc.).

Beyond that, some of the first songs I learned how to play included the Red Hot Chili Peppers' "Scar Tissue," Aerosmith's "Dream On," and the intro to Jimi Hendrix's "Purple Haze," none of which are overly difficult to learn, and help grow a sense of familiarity with the fretboard.

/My two cents