$lookup = Get-ItemProperty Registry::HKCR\.[a-f]?? |
  Select-Object -Property PSChildName, '(default)', ContentType, PerceivedType |
  Group-Object -Property PSChildName -AsHashTable -AsString

PS> $lookup.'.avi'

PSChildName         (default)           ContentType         PerceivedType     
-----------         ---------           -----------         -------------     
.avi                WMP11.AssocFile.AVI                     video             

PS> $lookup.'.fon'

PSChildName         (default)           ContentType         PerceivedType     
-----------         ---------           -----------         -------------     
.fon                fonfile                                          

Registry::HKCR\.*