Hopefully this is in the right section.

Anyways just as the title says I am looking for songs that are tricky to play and sing at the same time. Mostly acoustic song writer stuff. I need to broaden my horizons a bit and get out of my normal rhythm , thanks for any song suggestions!
Megadeth stuff..?

There's a lot of stuff really. But maybe those examples aren't so much singing.
No offense to you blazing riff and iSouLeZz but he was asking for singer song writer stuff. Not how to sing and play heavy metal/rock n' roll.

In regards to OP I have a few suggestions if you want to "Break out" of your usual Rhythm.

My first suggestion would be to try singing over finger picking patterns. Don't even need words just different vocalizations over arpeggiated chords. Practice alternating bass/melody lines and even just singing "La la la la La la la" over top will help you to develop, it could even help to inspire some future song you'd like to write.

Also reducing your guitar playing and working more on your vocal timing could help to. Using a simple 4/4 measure play a chord and let it ring out for the entire length of the bar while singing over top of the resonant chord. This would allow you to practice keeping time with your voice (It's still an instrument that needs to be learned) While using the guitar as accompaniment. (Playing minimalistically reduces the amount of concentration used on the guitar allowing you to focus more on the voice)

As for songs to learn that may help I'd recommend using rock and folk tunes from the 60's. Generally had simple enough guitar but enough alternating rythm's. Learn some Beatles, Zepellin, Jefferson Airplane, Jethro Tull, Pink Floyd, Simon & Garfunkel etc. They all have an extensive catalogue of songs for you to choose from that would help.
Always found All Apologies by Nirvana kinda tricky to play and sing at the same time.
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All Apologies - Nirvana

It's a pretty easy song but it took my a while to sing and play it.

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