Get all extensions and their respective file count in a directory

/var/cache$ sudo find ./ -type f | grep -E ".*\.[a-zA-Z0-9]*$" | sed -e 's/.*\(\.[a-zA-Z0-9]*\)$/\1/' | sort | uniq -c | sort -n
      1 .6
      1 .cache
      1 .noconf
      1 .php
      1 .sl
      2 .bin
      2 .el
      2 .tdb
      4 .baseA
      4 .baseB
      4 .dat
      4 .DB
     27 .db
    221 .deb

Here is the explication:

find ./ -type f

find only file, not directory

grep -E ".*\.[a-zA-Z0-9]*$"

filter file with extension

sed -e 's/.*\(\.[a-zA-Z0-9]*\)$/\1/'

delete path and file name, save only extension

sort | uniq -c | sort -n

sort, uniq and sort

Since you're using Linux (gnu grep), this is a good time to use Perl REs (PCRE) -P and grep's -o option. Taking @bindbn's answer as a great candidate:

find . -type f | grep -Po '\.([\w\d])*$' | sort | uniq -c | sort -n