Use exactly what is recommended by Lexus as listed in your owners manual.
The 2008 Lexus IS-250 runs on premium unleaded (required).
The 2008 Lexus IS-350 runs on premium unleaded (required).
The 2008 Lexus IS-F runs on premium unleaded (required).
The 2008 Lexus GS-350 runs on premium unleaded (required).
The 2008 Lexus GS-450H runs on premium unleaded (required).
The 2008 Lexus RX-350 runs on premium unleaded (required).
The 2008 Lexus LX-570 runs on premium unleaded (recommended).
The 2008 Lexus LS-460 runs on premium unleaded (required).
The 2008 Lexus LS-600H-L runs on premium unleaded (required).
The 2008 Lexus IS-250 has a 6-speed manual.
The 2008 Lexus IS-F has a 8-speed shiftable automatic.