The Pro Unit with a 60GB HDD will give you everything you need to get started except for a LIVE membership, actually it comes with a 30 day trial when you go to join LIVE, other than that, you can look for deal on Amazon.com for 1 year card, normal price is $50 USD. Sometimes you can find them as low as $30.
But you will want a HDD for game saves and such, ethernet cable and a headset all of with come with the 60GB unit. The Elite which has a 120GB HDD also comes with a HDMI cable.
Depending on how serious you decide to get with your gaming, you might also want to look towards a set of Turtle Beach X4's. Its a headphone with mic built in. Worth the $200 if you play late at night and dont want to disturb others and you can hear a bit better unless you have a nasty surround sound setup.
Elite with 2 free games
http://www.bestbuy.com/site/olspage....=1218085597958
Regular Elite
http://www.bestbuy.com/site/olspage....=1172881999620
Pro Unit
http://www.bestbuy.com/site/olspage....=1215818957702
1 yr LIVE card
http://www.amazon.com/Xbox-360-Live-...7367373&sr=8-1
I just selected Best Buy, you can get any of this just about anywhere though...
Good luck...