+1 for Ubuntu. A friend of mine said he had a lot of trouble getting git installed on CentOS 5...I think he even gave up on it.
+1 for RubyMine. I migrated from Aptana Studio to RubyMine and I think I'm sold. Aptana is just too bloated for my liking. RubyMine has great code validations and helpers. I've also briefly used Netbeans...I'd go back to it before Aptana. Also, you can try RubyMine for 90 days after installation...fyi.