There have been a bunch of great deals I've stumled into over the years. The two most memorable: The complete Greek 1967 set including the 50 and 100 Drachma in silver and the 20 and 100 Drachma in gold for $750. I dumped the silver coins on eBay (I now wished hadn't done that) and sent the gold in for grading. The 20 in gold; MS67 the 100 in gold; MS68 and possibly the finest known. The dealer who listed the set in his World Coin News ad told me later that 150 people called-in about the set after the ad appeared, and I just happened to be the lucky guy who got through first. This was back when gold was 400 an ounce. Probably the best deal recently, was the purchase of a 1937 Albania 20 Franga in AU for $425 that was sold by one of the majors with no photo in his listing on his own website. I figured it was priced right, would easily sell for double that on eBay, and in the event there was a problem with it he accepted returns. You can imagine my surprise when the coin arrived and it had that magical little word on the reverse spelled "P-R-O-V-A" which pretty much made the coin worth close to 10 times what I had in it with a mintage of 50 pieces.
Nothing spectacular, but for a young and new collector.. it made my day! Went to a local coin show and grabbed a few coins out of a bargain bin.. 75 cents each. Grabbed 3 buffalos, 3 v nickels and 3 indian cents. When i got home I noticed the date was really really worn, but it ended up being a 1913 raised mound buffalo. Pretty neat find for me