I've just bought off the 'bay a couple of cards that looked unfamiliar to me. Now that I have received them I was right. Neither card appears to be listed in any of the regular sources (Jeff, PCE or the Encyclopedia).
Anyone know anything about them?
The Caterpilla card is interes6ting as not only it got an 'insert' look about it, it also has the number AGW-5 on the back which hints that it is one of at least 5
Here's the scan:

The other card is printed on quite thin paper.

There are 10 cards in that series, AGW-1 THRU AGW-10. My set came packed in a really cool wooden box with a slip-off top along with a $15.00 phone card. I don't know if they were commercially available or an internal give-away. I'm leaning toward the latter because of its packaging.

There's a closed auction (and an older one on Worthpoint) for the "CAT Ag Products" wooden box. There are no mentions there on how they were distributed, but I don't see any sign that there was an "Earth Movers III" card set where the AGW cards would have been intended as inserts. (Plus, the woodgrain design on Sean's card would be a tie-in to the box.) So maybe they weren't an "internal" give-away, but possibly the box (with contents) was a trade-show special.

Google debris insights: "'I don't care who you are, you don't throw trading cards away,' said Tom Munson, president, TCM Associates, Des Plaines, Ill., creators of Deere & Co.'s 1994 series and Caterpillar's card program." This is a fun quote from an Advertising Age article from 1995 before they figured out that the bottom was falling out of the market.