In reply to jonnybmac:
The difference between EN 566 and UIAA 104:
2. Requirements for Slings
2.1. The UIAA Label can only be granted for slings that meet all the requirements of EN 566:2006, with the following exception:
2.1.1. No EN number required.
2.2. For the award of the UIAA Label, the following additional safety requirements shall be met:
2.2.1. Safety Requirements
If slings are made from tape by stitching the tape, at least 50 % of the visible area of stitching shall contrast with the tape in colour.
2.2.2. Test Methods
Check by visual examination that the requirements according to 2.2.1. are met.
References:
http://www.theuiaa.org/upload_area/Safety/Standards/Safety-Standards/UIAA_1...
http://www.hamradio.si/~s51kq/photo_album/Climbing_and_Mountaineering/pdf_c...
TL;DR: Buy Ocun slings. They are cheap.