For those of you out there who are interested in things like this, Garrys Mod (MotY 2005) is now available via Steam for the incredible price of $9.95 (Plus tax) if you have a Steam game already installed, or as a bundle with CS:S for $24.95 (Again plus tax).
If you're curious about how this affects its standing on Mod DB, we will still continue to support this as it is a modification of the original engine. It is, however, now listed in the games section which will enable you all to add your own mods (Modmods?) and addons to this site and our sister site, Addon DB.
As a side note, Steam now accepts PayPal for purchases so all you people stuck with debit cards and bank transfers can buy games.