PdaNet+ shares your phone's Internet with your computer or tablet through USB, WiFi Hotspot or Bluetooth. That will save you a $20/month tether plan. No rooting is needed.
The USB mode in PdaNet+ should support almost all Android phones. It also has a Hide Tether Usage feature that can be used when necessary.
WiFi mode (FoxFi) turns your phone into a WiFi hotspot but it only works for some phones.