Now that you have rooted there are many things you can do but one of the biggest is flashing a new rom. What does this mean exactly? It mean installing a new operating system on your phone. You can find these online in many different places like rootzwiki and xda. So if wanted the latest version on android you can get it. Now a few recommendations before you flash a new rom:
1. Back up your current OS by creating a nandroid. This will vary depending on the type of recovery rom you have installed. I personally prefer clockworkmod.
2. Find a good ROM. I have tried about 10 different. The most popular are cyanogenmod (cm or cmod) and AOKP. Here is a good article that breaks these down
3. Install it and have fun.
4. Once you flashed the rom remember to install the latest gapps package. This refers to google apps such as gmail, etc.
If you are curious how to flash a rom this depends on your phone and recovery software you have installed. For most phones you will boot into recovery and flash away.