I present now my own take on the Eldar Harlequins. This list is based primarily off of the Citadel Journal list that was created for 3rd Edition Warhammer 40,000 if memory serves, but has been influenced heavily by my reading of the old 1st & 2nd Edition rules and fluff, as well as various fan-made Harlequin lists that I have read at various times. There is nothing ground-breaking here, but I believe I have reached a point where the flavor of the Harlequin list is quite interesting - they are even more fragile yet deadly than their Craftworld cousins, with a few interesting quirks thrown in for good measure. This list has been playtested a bit, but I'd love to hear what other people think about it.
There are two options for downloading the codex. You can get it from either Scribd.com or Box.com
EDIT - New revision of Codex added/updated 04/16/2012 - see the links above for the latest version!