Meet my hallway. This photo shows how we inherited it a year ago, replete with four typical IKEA halogen bulbs, each sucking up 80W every time I came home. While I swapped out the rest of the house's lighting for low energy alternatives, I procrastinated with these ones because they have those pointy MR16 fittings and I couldn't find any compatible mini-sized CFLs (what we all tend to call energy-saving bulbs). I then had a look for the other green alternative: LEDs. After some laborious searching, I ended up ordering some £4.49 ones from the ever-useful energy-saving site, REUK.
The result is my hallway now uses 4 watts -- a twentieth of the 80 watts it previously used. There is, however, a downside. The colour temperature of the lights is now more white than yellow. More Lives of Others interogation room than Welcome Home hallway, but I'll live. See the photo on the left. It's also a fraction weaker on the illumination front but, again, I can cope with it for the energy savings.
There are better, more expensive LEDs out there, and the wonderful nature of the technology is that you can get them with any colour temperature. So I should really have simply shopped longer for a warmer and more powerful one. The best one I found on my searches was the warm 5 watt one here (pictured left), but after VAT and postage was added, it cost £30 a pop. As obsessed with carobn-cutting as I am, I'd rather pay £18 for four with a compromise and be done with it! If you find some that are a compromise between the two, let me know.
3 Sept 08 update: I ultimately found the lighting too white, so I've replaced the initial LEDs with three new warmer LEDs from this eBay store. The light is far more yellow in hue and closer to the colour you get with halogens. In fact, my only criticism is they're slightly too yellow (see photo below). They cost £9.12 each.
For the voltage reasons described by REUK, I've had to keep one halogen in the circuit. So I've now got one 20 watt halogen and three 3 watt LEDs, consuming a total of 29 watts. Even with the single halogen, that's much less than the 80 watts from four halogens.