I was going to put these on my GS, but sold it before I could get round to it. I was horrified by the price of additional lighting from people like Touratech, so I went on a hunt for a cheaper alternative. I eventually found these on eBay UK, for the princely sum of �33 to my door, for the pair.
Cree LED Motorcycle Lights
I fitted them today. They mount onto the engine bars just fine, although as the brackets aren't adjustable it needs a bit of care to find the right spot to hang them. They give a very focused spot beam, so they need to be pointed down to avoid dazzling oncoming traffic. But pointed forward they are brighter than the dipped headlight, so I'm sure they are going to be noticed. I think they will be more of a conspicuity aid than a driving light, but that's OK. Mounting them low (I couldn't find anywhere else without making a separate bracket or lighting bar, no thanks) means they make a very distinctive triangle to oncoming traffic.
They are built down to a price, and the mountings are fairly flimsy. I may well take them back off tomorrow and beef up the points of attachment. But they are (supposedly) waterproof and only draw 30W between them, so they shouldn't trouble the generator too much. I've wired them into the sidelight/indicator circuit, so they are on with the ignition.
I'll report back when I have used them for a week or two. Both morning and evening commutes are in darkness at this time of year, and on fast and unlit roads, so anything extra has to be a help.