Lights

Sorry, I disagree. I'm with Tiswas, and others on this. In cycling experience and expertise, hippy is 1,000 miles ahead of me. But as far as commuting is concerned, I know a thing or two also.

These are my musings on the matter.

A 1 watt front light is the bare minimum that should be used a be-seen light. It can't be used as a light that illuminates one's path, as it is far too weak for that. 1 watt lights have an output of normally around 70 lumens.
http://direct.tesco.com/q/R.211-8780.aspx
http://www.chainreactioncycles.com/Models.aspx?ModelID=55127

http://www.winstanleysbikes.co.uk/product/46291/NiteRider_Mako_1_Watt_LED_Front_Light

Next up the evolutionary ladder is the 3 watt front light. These have an output up to somewhere around 200 lumens. This is a very bright light for commuting. It is still best as a see-me light, but at least this light can also illuminate your way, but since most of these lights are quite directional, when pointing them downwards, they obviously lose their effectiveness as a be-seen light.
http://www.saltdogcycling.com/bike-lights/one23-mega-bright-3w-front-bike-light/
http://www.highonbikes.com/rsp-asteri-3-watt-1-led-front-bike-light-rechargeable-laa910.html
http://shop.grahamgoode.com/led-lenser-m7-front-bike-light-torch--cycle-holder-220-lumens-836ft-strobe-sos-morse-64802-p.asp

There's then another step up to the mid-powerful lights, and some torches, of the 250-300 lumens range. All are very powerful, and cast a lot of light. But again, very directional in the main, but can definitely be used for road illumination and at a very good speed, but not for fast night riding off-road.
http://www.discountcyclesdirect.co.uk/product_info.php?products_id=11647
http://www.chainreactioncycles.com/Models.aspx?ModelID=70072

http://www.ribblecycles.co.uk/sp/road-track-bike/Lights-and-Lighting-Systems-Hope-Vision-1-LED-Universal-Front-Light/HOPELIGH100

Another incremental step up is the 450-600 lumens brigade. This is interesting, as the light is sufficient for all needs, whether snow, fog, heavy rain, or pitch dark. But it appears that cramming this much power into so small a unit is not without difficulty. The Light&Motion Urban 500 in particular does either lower the output or cutout when overheating. Some others have also shown similar issues. Its worth investigating before parting with one's readies.
http://www.allterraincycles.co.uk/product/125624.html
http://www.swinnertoncycles.co.uk/ProductInfo.aspx?productid=EH8560415A
http://www.chainreactioncycles.com/Models.aspx?ModelID=70831

Anything more powerful than these are normally battery-plus-wire-pus-unit jobbies. I'm not a fan of wires, and the selfcontained units are the best options for cummuting, due to their ease of removal at the end of a journey. But the battery pack lights offer lighting that not just can match a car light, but far, far, far exceed it. Essential for night rides in forests, but also for longer rides on a low level, so maximising runtime - the Dunwich Dynamo comes to mind.
http://www.chainreactioncycles.com/Models.aspx?ModelID=75282

http://www.chainreactioncycles.com/Models.aspx?ModelID=70458

Last and not least, there's the commuting-specific lights. These are newer and very powerful lights, but they are all designed to cast a light that only points downwards, and do not dazzle car-drivers. I was going to stick this in anyway, but it seems more apt due to recent comments above. There are 3 lights at the moment that fit this particular criteria:
http://www.cyclesense.co.uk/m60b189s308p12233/BUSCH_and_MULLER_Ixon_IQ_Rechargeable_/RS_GB
http://www.mcconveycycles.com/store/product/15378/cateye-econom-force-rechargeable-hl-el540-front-light/
http://www.tredz.co.uk/.Trelock-LS-950-LED-Rechargeable-Front-Light_44423.htm
Review and compare these last 3 here