You might find this site useful.
http://www.kulekat.com/led-home-lighting/led-replacements-for-halogen-lamps.html
I haven't tried any of them but I am currently researching the lighting for my new house and would like to go LED if possible. The Zenigata ones from Sharp seem to get some good reviews and have a wider angle than many.
Brightness is obviously an issue. Standard incandescent light bulbs produce about 15 lumens per watt (lm/w). Halogen downlighters are about the same, some worse, some better. Compact fluorescents produce about 60 lm/w and LEDs are about 45 lm/w. So if you want to replace a 50w halogen (producing about 750 lumens) with an LED then you will need about 16-17 watts of LED. The 4.5 watt Zenigata LED is being marketed as a replacement for a 35-50w halogen. Sharp's marketing about it is here
http://www.mouser.com/pdfdocs/sharp_ZENIGATA.pdf. I haven't tried it, but to me the maths don't add up for it to be a 35-50w halogen replacement. The sellers that I have seen (e.g.
http://www.yourwelcome.co.uk/acatalog/led236.html) reckon that it produces 200 lumens. A 35 watt halogen will produce 525 lumens and a 50 watt halogen will produce 750 lumens. I have no doubt that LEDs will develop rapidly. I think I read that Sharp have LEDs in the lab now that produce 130 lm/w but no doubt it will be a few years before they are in the shops.
There are a couple of other things to bear in mind. Firstly you need to be aware of the colour temperature. If you want a light that will be more like an incandescent or halogen bulb then you need to go for a warm white bulb (anything with a colour temperature below 3000K) rather than cool white. Warm white bulbs unfortunately produce fewer lumens per watt than cool white.
The second thing to be aware of is that if you are replacing low voltage halogens with LEDs then you may need to change the drivers for the lamps (see
http://www.yourwelcome.co.uk/acatalog/12v_Lamps.html ). If you don't, then the lamps will probably fail before they get anywhere near the hoped for 40-50,000 hours.
The third thing is that, although LEDs are a lot cooler than halogens, they do need to be kept cool. If they get too warm then their lifespan will be reduced considerably.
If I was you, then I would try a couple of replacements for the 240v lights and see what you think (and please let me know!).