I use twin Blackburn Fleas (Li-ion LED lights) mounted to my fork stanchions (vertically) which gives a frankly awesome beam spread in front of you - with a brighter patch in the middle where the beam edges cross.http://www.chainreactioncycles.com/Models.aspx?ModelID=57982
Can be complemented by use of a Maglite/similar handlebar-mounted (which can be set more easily to flash than having to reach down & press the buttons on the Blackburns - tho you get used to that pretty easily.) The bad news is these are not 'cheap' (15-20 quid each) but are USB & mains rechargeable, which means they can be recharged at work from your desktop or a plug with a mains-USB adapter. They won't give a distant beam further than about 30ft, but a wide beam spread (with two). I use mine on towpaths & lanes & never had any issues. Also bright enough on full twin-beam to get cars to give you right of way if you're heading towards them on a lane!
Real-world size is about 2" by 1.5" so they don't weigh 'much'! Velcro fastenings tho, but they are sturdy and convenient, I guess, just take care to do them tight enough!
Wouldn't recommend if you're in unfamiliar territory, but if it's a commute the chances are you know the route!
2013 On One Scandal | 2011 Ghost ASX 3700 | 2008 Magura Test Bike | 2006 Raleigh RS950
1999 Voodoo Hoodoo | 1999 Raleigh RSP 450 | 1997 Giant ATX-D 990 | 1997 Ghost X-700
1995 Giant Cadex MCM-3 | 1995 Voss Ti | 1993 Giant Cadex CFM-2 | 1992 RS Topline Mammoth