I'd have to go with Rust, Countdown and Youthanasia.
Rust In Peace. Get it. Now.
Moar Grateful Dead:
Led Zeppelin (I can dream, can't I?):
Rust in Peace.
Just about any of the first five albums are great starting points, but I recommend after going with Peace Sells, move to Rust in Peace.
UA is a good listen, but it isn't classic Megadeth worthy. I'm not saying take it away from your choices, but listen to it after you listen to the first five.
^is a WoW fanboy
^^is pointing at himself
^^^used two carets
Countdown to Extinction is my favorite. I love pretty much every song on there. Rust in Peace is ok too.
Megadeth. Upsetting Parents since Killing was its buisness.
though it's funny how most early megadeth fans who were teenagers or young adults are parents now with teens.
Get Killing is My Business; it's awesome (it's also arguably the closest thing they have to Peace Sells that isn't Peace Sells). So Far... so Good... so What! is another great choice.
If you like those two, Youthanasia and Countdown to Extinction're great, and The System Has Failed is worth at least a listen if you liked the other five I've mentioned. I loved it, but it's nowhere near Peace Sells, even though they share a guitarist.
Oh, and Rust in Peace is okay, I guess. Overrated as hell, though.