Recently sent my best half dollar roll-searching find to John Wexler of doubleddie.com (a quite famous coin variety and error researcher...we're talking one of the guys who writes the books.) It's a 1977 D DDO-001 Kennedy Half graded MS62 by NGC. For those of you unfamiliar with "things coin," coins are graded on a scale of 1-70, with 70 being perfect. Anything graded MS (Mint State) means it is uncirculated, and usually commands a premium from circulated, or lower-grade, coins.
In any case, I recently wrote an article on the 1977 D DDO Half (that appears here.) I had been in contact with Mr. Wexler for another coin find of mine that he needed better pictures of (a 1960 D/D RPM-002 Lincoln Cent.) After he informed me that he did not have an example of the 1977 D DDO-001 for his files/website, I offered to send the coin to him. (I've found his website an invaluable reference, so anything I can do to help make it better is an honor!) In any case, here is a link to the page where my coin is referenced.
In case anyone is wondering, I currently have found six examples of this scarce variety: an MS62, an UNC Details (Scratched), an AU58, and 3 more found after the original coins were submitted. Since I found them hunting through bags/rolls of coins from the bank, I've paid face value for each...not bad considering I'd value the MS62 between $250 and $300. The last 3 I've found will probably grade in the low AU range.