So you've used Part 1, Part 2, or Part 3 of my Rooting Guide to root your Android phone. And once it was rooted, you didn't immediately run for the hills and unroot it. So what now? What can you do with a rooted phone? More importantly, what should you do with a rooted phone?
The benefit of rooting your phone is the ability to install ROMs, which let you tweak and modify options that weren't initially available. The first thing you need to do is hit up Android Market and grab ROM Manager, pictured above. That link will take you to the Android Market page, or you could just search the market using your phone. The link I provided takes you to the free version of the program, but there is a premium version available for $5.99. For the sake of this article, I'm going to assume you're as broke as I am and use the free version. Besides, since we're just learning, the free version will do just fine.
Once you've got ROM Manager installed, fire that puppy up. At the top of the screen you should see "Flash ClockwordMod Recovery." This is crucial for backing up and restoring your phone in the event that something goes catastrophically wrong. Peace of mind goes a long way. Click the Flash button, confirm your phone model, and then watching the progress bar at the top of the screen do its thing. Once it's done, it'll let you know.
To download CyanogenMod, in ROM Manager click Download ROM and then find CyanogenMod in the list. You'll have the option to choose which version, I just chose the latest. (NOTE: Do not grab CyanogenMod Nightlies, at least not at this time. These are experimental nightly builds that, as the description itself reads, are probably broken.) Once you click the download button, you'll be asked what addons you'd like. Select Google Apps, as this contains all of Google's proprietary apps. Once it's done downloading but before it installs, it will ask you if you want to backup the existing ROM and wipe the data cache. You want to check both of these options.
IMPORTANT: You should've already done this before even rooting your phone, but if you have any data on the phone that you want to keep - pictures, videos, contacts, etc - back that up before proceeding. I recommend manually backing it all up.
It's important that you wipe the data and cache when you do this. I tried installing without doing so and my phone just got caught in a CyanogenMod boot loop, which forced me to factory reset.
Once it all boots back up, you'll be asked to sign into Google. Bask in the new and alien look your phone sports! CyanogenMod comes with plenty of applications, as well as new takes on existing apps. I spent a fair amount of time sifting through it all. The sky is now the limit. To infinity and beyond, etc etc. Enjoy your rooted phone!