Loading compressed texture data directly

What format do you use? How do you do this? Is there a program that will convert standard image files to some compressed format that I can load directly, instead of wasting time compressing everything at runtime?

Actually, forget that, I don’t want to lose the ability to load a texture at different resolutions. That’s probably why Doom 3 and HL2 load so slowly.

Unless you stored the mipmaps and used the first mipmap for the first lower LOD.

Okay, tell me how.

Take a look at the dds file format (check msdn, it’s a directx file format, but the compressed texture format is used by gl as well).
Also check out

Google for “dds viewer” to find some conversion programs (if you don’t want to roll your own). DevIL supports dds compression as well.