When I started, I learned:

Lithium,
Heart Shaped Box,
Karma Police,
China Grove,
Sweet Home Alabama,
Freebird,

...I think it's safe to say that I haven't played any of those songs in years. That was before I learned Paranoid Android and my head disappeared so far up my arse, I couldn't see the light of day, much less learn a new tune for a long time.

peace,
-nick

they're not impressive but every guitar player should know at least these songs. they spice up any dying jam. whether or not it's to rock it out or fall over laughing at the cheese you just pulled out.

steppenwolf - born to be wild / magic carpet ride
led zep - dazed and confused / communication breakdown
sabbath - iron man / sweet leaf
skynyrd - sweet home alabama
CCR - proud mary
iggy and the stooges - i wanna be your dog
nirvana - smells like teen spirit
neil young - rocking in the free world

for the most part they're 3 chord songs. heck most of rocking in the free world is E hahaha. don't let the simplicity fool you though, they're exactly the kind of songs that just about everyone has heard a million times with melodies and changes simple enough that most people could pick them up relatively quickly in a impromptu jam session.

If you truly learned or are learning to play,every guitarist should know how to play 'twinkle twinkle little star' and not tab either haha.That was the first song I ever learned.

The first song my friend learned was '100 years' by Five for Fighting... so yeah...

Well I'm just starting... so some songs that I'm learning are

Karma Police- Radiohead- A great song to play, taught me some new chords

Ziggy Stardust- David Bowie- Really fun to get right, and can help with double picking

Mr. Jones- Counting Crows Fun to sing along with

Anything by Neutral Milk Hotel- These songs are so simple to learn but can help early on with strumming patterns and easy chords

Anyways these are just some songs that I have learned, and I've enjoyed them so far.

Great ones of varying difficulty:

Dick Dale & the Del-Tones - Misirlou: A great gateway into alternate tunings.
Miles Davis - All Blues: Learning this song totally changed how I thought about playing music.
The Smiths - Bigmouth Strikes Again: Feel good about yourself by playing easy chords fast.
R.E.M. - Driver 8: How to arpeggiate like Mr. Peter Buck himself, the best right-hand in the business.
The Clash - I Fought The Law: Mick Jones: Making crappy guitarists all over the world just a little more badass.
The Jam - That's Entertainment!: Probably the best song to learn first.

What chords are used in this song? Love that tune.

Bigmouth Strikes Again Chords (ver 2) by Smiths @ Ultimate-Guitar.Com

Easy chords, great tab. You need a capo mind you, or it really won't sound right.

Neon Knights - Black Sabbath
Excellent groove to the rythym guitar and a wicked lead solo. A definitive "gotta learn" song.

I could just barre the fourth fret with my first finger too,right? I can barre all the frets pretty easy,its the first fret that really takes alota balls tho.lol thanks dude.