For TB v0.7 thru v9.* Rated 5 out of 5 stars

Get SmilieInserter Plus by Throoper. It rocks...
https://addons.mozilla.org/en-US/thunderbird/addon/smilieinserter-plus/

Brilliant! Rated 5 out of 5 stars

Brilliant! I love this plugin! Many many thanks Throoper!!!!
Can't wait for the TB 8 version.
For TB 7 get the download from http://www.megaupload.com/?d=6IEORKOF

Rated 5 out of 5 stars

@Jogar the Barbarian
Thanks for creating and hosting this update (http://supersilly.com/~greg/storage/smilie_inserter-0.7.0-tb.xpi)
You rock!

FWIW:
Working in TB 3.1.9.
For folks worried about malware:
I scanned the xpi with Malwarebytes before install, and did a system scan after install, it's clean.

Many thanks!!!!