Ars Technica reports that the latest beta version of iPhone OS 3.1 contains reference to two currently unknown products, "iProd0,1" and "iProd1,1". Reference to "iProd0,1" was first spotted back in March, but "iProd1,1" is a new addition.
Ars speculates that "iProd1,1" could be the heavily rumour Apple touchscreen tablet, although Ars weighs doubt on the ability for iPhone OS to run on a tablet and adds that the product designation could refer to the new iPod nano.
[Edit] The above screenshot also references iPhone3,1 suggesting a new iPhone is also being testing with this latest iPhone OS release. The current iPhone 3GS is listed as iPhone2,1 whilst the iPhone 3G and original iPhone are iPhone1,2 and iPhone1,1. The first number generally represents a major hardware change such as a new CPU.