First month of service FREE from Vaya on any Flexi or Unlimited plan. Website states Online Only
The $20 Starter Pack is waived if you sign up for 24 months - I would not recommend this.
Similar to the previous promo deal posted here http://www.ozbargain.com.au/node/81590
I'm personally on the $17 plan and have enjoyed their service thus far. I signed up during the previous promo and a credit is applied to your account to the same value as your selected plan.
Previously an LC customer, I prefer Vaya mainly due to the phone support (even though it's offshore). Also I believe LC recently jacked up their prices. A good pro/con list is provided by Spizz: http://www.ozbargain.com.au/node/81590#comment-1053458
Vaya's website isn't the greatest but still gives you everything you need. In terms of app support the full version of myUsage supports Vaya. I currently use it and it works well. Alternatively you can use http://mobile.vaya.net.au/ which is more intuitive and cleaner than the desktop version!
Edit: Thanks to Holysmoke for providing this independent FAQ link https://vayafaq.jottit.com/
Last I checked there was no Plan change fee, but best to call and verify.
Mod: referral links not permitted for new users
Extended to 28/2/2013