So... as you can see lots of options, let me break it down for you, as I see it.
Option 1: You can get cheap as chips "deal extreme" type bike "P7 LED" lights for £50 from Hong Kong (short delivery times now, long as the nights draw in). These are also available from UK suppliers for a premium.
These are great units, cheaply made so aren't as reliable as the 'big guys', but have plenty of light & I highly recommend them. Theory being if it break, buy another you can buy 5 to most large manufacturers one £250 unit.
Mine has done me sterling service, though have had to replace the protection circuit on the battery (cheers Smudge) on it's 2nd year and put a new connection on the head unit after the wires frayed (couple of quid and bit of easy soldering).
There are also plenty other Hong Kong manufacturers supply similar kits, with newer & better XP-G or XM-L LED's fitted. The XM-L's will be this years top sellers IMO. I've bought one off Smudge (tad more expensive than from DX), as I can't help myself with cheap but brilliant lights, and it's immense, a great unit.
If you want a cheap way into night riding or just cheap night riding, then one of the above is a great options IMHO.
Option 2: You buy from the 'known' manufacturers, the likes of Lumicycle, Hope, Lupine. Usually great lights, very reliable, but unless you buy the all singing and dancing top model, they tend to be no brighter than the DX units for 5 times the cost. They also "tend" to lag behind badly when it comes to the newer LED technologies. Buy if you want 'real' piece of mind & backup.
[Personnally I had a Lupine unit a few years back and found them to be rude and unco-operative, especially considering their premium prices, but others love em]
Option 2 (B): Exposure lights, all in one units that are very convienent but very expensive with it, but loved by there users.
Option 3: The custom makers, the likes of Troutie and Luminous and others. Making it themselves using the latest and greatest LED technology. You pay a premium, but will get quality unit (hand made), which the guys will happily support (.. if you break it) or upgrade later, if you want. I have a Troutie Mini, fantastic unit, but I paid a premium for it VS the DX units (DX weren't as bright at the time though).
One of those options should/will appeal to you personnally (cheapness/support/real quality), choose it and run with it.