A good collection of standard holes sizes are included in ISO 273 Fasteners -- Clearance holes for bolts and screws.
You can look at drill manufacturer catalogs to see standard products. Emuge, OSG, Kennametal, and Sandvik have a lot of information.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.