This may be a little excessive, but I think it could be very organized:
Completed maps, HL1 (below are sub-categories)
-Counter Strike maps
-Half Life/Sven Co-op maps
-Official mod maps
-Other mod maps
Example maps
-Source Exmaples
-Half Life 1 examples
Problems maps
-Problem maps
Unfinished work
-Counter Strike
--Alpha releases
--Beta Releases
--Dicontinued
-Half Life/Sven Co-op
--Alpha releases
--Beta Releases
--Dicontinued
-Official mod maps, unfinished
--Alpha releases
--Beta Releases
--Dicontinued
-Other mod maps, unfinished
--Alpha releases
--Beta Releases
--Dicontinued
Completed Maps, Source
-CS:S
-Half Life 2
-Other Source maps