Here are some cool Android ROMS that you can checkout.
Note: The Author of this post is not responsible for bricked devices, burnt phones or dead androids. Read the article about ROMS here: What is a rom?

Well, if you know what a rom is, then proceed:

Cyanogenmod


CyanogenMod is an aftermarket firmware for a number of cell phones based on the open-source Android operating system. It offers features not found in the official Android based firmwares of vendors of these cell phones.
Quick links:
Read more about CyanogenMod
Get CyanogenMod now! 
Watch a video tour


MIUI


MIUI comes 2nd in popularity in the ROMS.It comes with a lot of features for a large variety of phones. It is well known for its notifications, extended apps, etc.

Quick links:
Read more about MIUI
Get MIUI now!

Slimrom


Well, the name says it all. Slim rom is basically an AOSP rom, whose main feature is that, it is very lightweight and battery friendly ROM. Another fact is that, much of your phones stock features will be missing and that's the speciality of this ROM. Well, I have to say that it is my personal favorite. Currently a few phones are supported. See if your's is supported.

Quick links:

MORE ROMS COMING SOON!