I don’t provide JPEGs any longer unless the client specifically asks for one. I used to provide them, since they can be easily opened and seen by the client, but almost every client today can open a vector-based PDF. I’ve also found that JPEGs tend to proliferate and become the standard passed-around version within the company, which is never good. I see JPEGed logos as having no useful purpose and only supply them when specifically requested by the client. Even then, I only provide it with warnings against using it for anything.
As for what I do supply them, it depends on the situation. If it’s a small operation with no on-staff designers, I’ll give them both .ai and .pdf in B&W, grayscale, CMYK, RGB and Pantone colors. A .png is useful for websites and transparency, but I have no specific sizes and try to give them something in a range that meets their website needs. I’ll also supply them with large, high-res .psd’s.
Depending on the situation, I’ll also supply clients with a version for light backgrounds and one for dark backgrounds.
If the client is somewhat savvy about these things or has an on-staff designer, I’ll typically only supply them with the .ai and .pdf in B&W, grayscale, RGB, CMYK and Pantone colors. I figure they’re in a position to make their own format, size and resolution variations as needed.
In addition, at a very minimum, I’ll supply basic usage instructions for each in an attempt to help the client know what format is most appropriate for various purposes.