I remember going down to the local news shop in my town and buying these cool cards when I was young. They were stickers that spoofed common products. My friends and I used to actually make our own versions of Wacky Packages!
I found about 10 packs of unopened cards at a flea market, and it was really fun to see some of those cards that I used to laugh at when I was a kid. Those packs yielded about 3/4 of the 1979-1980 third series. I also own a complete set of 1986 Wacky Packages, which were basically reissues of classic cards from the '70s and the complete 1991 set that had all new cards for the 90s.
I also found an uncut sheet that features two sets of the 1979 first series cards. Apparently the sudden glut of these sheets available to collectors was due to a large find in a warehouse in the 90s. These cards aren't actually the originals. Find out more here: http://www.wackypackages.com/sheets/1st_rerun.html
Here's a card that my friend found in a pack back in 1979 or '80 that I always coveted:
These things have really become collector's items. While I'm not heavily into collecting them, I always check the card dealers at shows, Ebay and flea markets to see if they have some lying around. Here are some links to some great Wacky Packages pages:
Here's a great page maintained by Gregory Grant that has a lot of pictures and Wacky Packages history:
Here some other Wacky Packages linkst: