Golden presidential dollars are great to look for missing, slipped, and even doubled edge lettering. On the reverse a clash can be formed where it looks like another spike on Lady Liberty's head. Susan B. Anthony dollars look for 1979-P coins, there is a narrow rim and wide rim variety, I recommend you do some research on them. Quarters have nice die clashes, DDOs, DDRs, and other varieties and errors. I recently found a WHMR-001 1973-D quarter, just like that. Some recommended sites are doubleddies.com etc.