Making site usable both from Mobile devices and desktops

I have a website that I want to make look good from a non-mobile browser, but make very usable from a mobile device.

I'm thinking I'm going to detect if the user is likely using a mobile device, and if they are, redirect the first hit to a page that says something like: "It looks like you're viewing this page on a mobile device. Would you like to view the mobile version?" Based on the user selection, I'll set a cookie. (Would this be annoying, or helpful?)

But I'd also like to make sure that if I miss someone who is mobile browsing (if I think they're non-mobile, but it turns out they aren't), I provide some way to switch to the mobile version. Also, if I detect someone is mobile, but they'd prefer to browse the full non-mobile site, I need to allow that, too.

I'm leaning toward having a mobile and non-mobile version of every page on the site, just presenting the data differently (and with a lot less images, etc) for the non-mobile version.

Anyone who's been through this, have advice? Any links to sites that do this right?