Rachael,
Depending on your tastes, here are a few easy songs for the acoustic:
- Tom Petty's "Learning to Fly" - four chords (F, C, Am, G) in a repetitive pattern. Just the same thing over and over--but it sounds cool and it's great practice on four major chords.
- Willie Nelson's "Me and Paul" - three chords (A, D, E) with alternating bass notes (A/G, D/C). If you like Willie, this is a good song for practicing timing and alternating bass notes.
- Credence Clearwater's "Bad Moon Rising" - three chords (D, A, G) with variation on the chorus (G, D, A). Easy to play along with.
- Emerson, Lake and Palmer's "Lucky Man" - three chords (G, D for verses; Am, G, D for choruses). You can strum or fingerpick.
- Fleetwood Mac's "Rhiannon" - three chords (Am, F, C) in two combinations (Am and F on every other verse, C and F on the ones in between). This is easier to play than it might sound. Okay, so it has that cool guitar riff, but it also works as a rhythm/strum on the acoustic.
I've found these and many, many others right here on Chordie. (My first choice for guitar tabs/chords.) I just thought I'd suggest a few specific songs since you already got the "check a songbook" answer. Each of the songs I listed is great for practicing certain things on guitar--basic chord shapes, alternating bass notes, timing, mood, etc.
Good luck and I hope you make that guitar sing!!
Paul