IG Group (www.iggroup.com) have deployed Lightstreamer on their sites to provide their customers with live data.

Some of their publicly visible applications include:

IG Index (www.igindex.co.uk) - financial spread betting
IG Markets (www.igmarkets.com) - CFD & FX trading
extrabet (www.extrabet.com) - fixed-odds betting
binarybet.com (www.binarybet.com) - spread betting and fixed odds