[amagab]

I have a white iMac that works fine and have Lion installed. However, for some reason the wireless keyboard and mouse (both Apple products) will not connect until after I have logged in. I have to have a wired keyboard attached and use the arrow keys in order to login. Then while it's loading everything, the wireless keyboard and mouse connects.

This is not an issue on my other iMac nor has it been an issue on any other Macs I've owned.

What is causing this and how do I fix?

Have you ever connected these devices with another Mac/iOS device that is still in use in your home? If so, go to the Bluetooth preferences on those Macs and "forget" the keyboard and mouse.