I guess it all depends on your style.
Jazz (Big Band): OLD MAN RIVER, Frank Sinatra, Dick(s) Noel and Haymes, Bing and Bob Crosby. . .for something funny, try some Bob Hope (LOVE!!!!!!!!!)
Classic Rock : BACK CHAT, by Queen; almost any Journey song (personal favorite: SEPARATE WAYS, WORLDS APART. . . what a range!)
90s style Rock (not quite grunge, if you know what I mean): Blink 182, Nirvana
Country: Trace Adkins, Alan Jackson, Brad Paisley
And yes, I really listen to all this, not just throwing names out there:
90s boyband: N*SYNC
Jazz (Slow Dance Big Band): Glenn Miller tunes with Texas Beneke on vocals, Bing Crosby (again), Mel Torme, Fred Astaire(did some swing tunes too, like PUTTIN' ON THE RITZ, written by Irving Berlin)
You could also take your favorite songs and just octave down if needed. I do that all the time because I'm a girl with a tenor 2/baritone range. Just as freaked out about it as my teacher. :)