The Airport Base Stations either do or did until recently use an AMD-built CPU (at around 333MHz, if memory serves).
I think the Xserve RAID system uses Intel chips, and there are a variety of Intel-made chips on Apple's motherboards.
There's currently renewed talk that Apple's in negotiations with Intel about chips intended for Macs. There are several possibilities. One is that Apple wants to contract Intel to fab the core logic for their systems. Another is that Apple intends to buy chips for wireless networking from them (Intel holds a number of patents in that area, and going to them directly would avoid licensing fees).
The most interesting possibility stems from news from IBM, though. It seems IBM along with Sony and Toshiba, may be looking to liberally license the design of the "Cell" CPU. Intel has huge fabrication capacity, so Apple may be trying to convince Intel to get onboard the PowerPC wagon. It would be advantageous for Apple to have more suppliers, and it would be a good move for Intel, to solidify their presence in the embedded processor market. Somewhere around 98% of all CPUs sold go into embedded systems like Cars and appliances. PowerPC represents a singificant threat here to Intel's own Xscale CPU family, and Intel would be wise to hedge their bets and be a prime supplier for both types of CPUs.
I'm sure IBM doesn't like that possibility, but I have a feeling it's really in keeping with their long-term goals, which seem to be a slow conversion to an IP licensor extraordinaire, leaving the mundane production to others.