There is no official repository for Aptana in Ubuntu, so some manual steps are required in order to get Aptana to work. There is also a weird Unity menu display issue, fortunately this can be worked around by the custom desktop launcher created below.
Visit http://www.aptana.com/downloads/start and download the latest zip file of Aptana
wget (current as of time of writing)
wget -P ~/Downloads http://download.aptana.com/studio3/standalone/3.2.2/linux/Aptana_Studio_3_Setup_Linux_x86_64_3.2.2.zip
Unzip Aptana to /opt/aptana
sudo unzip ~/Downloads/Aptana_Studio_3_Setup_Linux* -d /opt -q sudo mv /opt/Aptana_Studio_3/ /opt/aptana/
Make sure you own it correctly (so updates will work)
sudo chown -R $(whoami):$(whoami) /opt/aptana/
Create the custom desktop launcher
sudo vim /usr/share/applications/aptana.desktop
and insert the following text:
Name=Aptana Studio 3
Comment=IDE for Rails, Python, PHP
You should now be able to find it in the unity launcher
Pinning it to the unity bar is a good idea
Hope this helps you, get cracking with Aptana in Ubuntu.