Try gumtree, where you looking to live?

Having just moved to Geneva, I find the London rental market a lot quicker -- but also more intricate.
Make sure you have a stroll around the area, because the differences between good and bad areas are a lot bigger there.
But I haven't heard many stories of people not getting the appartement they applied for -- sometimes you can even get them below the asking price. Most flats are vacant immediately or within the next two weeks.
On top of gumtree, try rightmove (which is a touch more commercial but has nice email alerts for hand-drawn search areas etc).
Go on either site, pick an area, talk to one of the agents with many properties there and they will guide you around. Don't expect them to do the work though. Always keep searching online. If you're lucky you find a private landlord, which is often cheaper than the agent.
Transport is an essential factor in London -- due to its size and (lack of) quality of infrastructure.
If you already know where youre gonna work, try http://www.mapnificent.net/london/ to find areas with appropriate commute times. (unfortunately not weighted by "pain"-factor of hot & smelly district line vs chilled-out DLR)

Good luck!

www.Spareroom.com also has flats as well as rooms.  Right Move is also popular.  Gumtree turned a bit odd recently compared to a few years back.  Or you can contact the estate agents directly depending on what area you wish to live in. 

As the post above states, agents tend to charge a lot of fees and take a large deposit, so sometimes it is worth going through a trustworthy private landlord,  rents are often cheaper this way as well. 

I vote rightmove.co.uk as well .. 99.9756% of agents are listed in rightmove, so rather than trawl through lots of individual sites, they're all together on rightmove.

Gumtree is more for private individuals or really small agents, flatshares and that sort of thing.

Although London is expensive compared to the UK market in General, it's cheap compared to CH.. What you'd pay for a rental deposit here would be a mortgage deposit in London, almost.  

I lived in Eltham, nice area, commuter belt, 20 mins train to center.. Then West Finchley, also nice, 10 mins tube to center.. Finally moved out to Harpenden, almost countryside with 45mins train to center.  Harpenden was by miles the nicest and cheapest but furthest commute. 

I would also recommend Rightmove and Gumtree, but you'll also need to put in a lot of time getting to know the areas of London that you might live in, as most of your research will have to be driven that way due to the large area and potential for long and expensive travel times.  (If you could give us an idea of where you will need to go for work etc. it will be easier to offer advice.)

If you have an option to stay in temporary accomodation for a while you should do it, as this will give you time to research properly.  You should also make use of any contacts you have in London to help you. 

Although, as others have said, the process of signing up for a rental is easier than Geneva, the market is very tight in London at the moment, so it will still take some money and effort.

Warning 1. There is a large chain of Estate Agents / Lettings agencies called Foxtons which I would encourage you to avoid.  I can explain more by private email if needed.

Warning 2.  There are lots of rental scams in London, most of which are aimed at people arriving from overseas or out of town.  Make sure you have the right legal contracts signed by the right people (the most common scams involve people renting out properties that aren't theirs) before parting with any money, even for a flat / house share.

Good luck!

Andy

Hi all,

Thanks for your recommendations.

I am moving to Roehampton, SW London. I have temporary staying for 1 week maximum. Couldn't find anything so far and I need to hurry up. 

Going to make a deeper research. 

Thanks in advance

Roehampton and the areas next to it are mostly quite densely populated and expensive. (I'm assuming that you don't have a large budget.)

If you will be depending on public transport, I would recommend looking in areas a few miles out to the west and north-west.  Brentford, Isleworth and Osterley are all nice areas with a lot of rental properties that are typically a bit cheaper than Putney, Richmond, Southfields etc..  You could also look at some parts of Kingston.  In all of these cases you will probably be depending on buses (which aren't bad these days) so have a look on: http://journeyplanner.tfl.gov.uk/user/XSLT_TRIP_REQUEST2?language=en

to see what the connections and journey times are.

This all gets easier if you get yourself a decent folding bicycle (I've been commuting with a Brompton for years, including in London) as you then don't need to live too close to a tube or bus stop, and, despite popular belief, cycling in London is safe and easy.

Best of all would be to get a motorbike or scooter (if you have a licence), as they are very cheap and easy to buy in The UK and will get you anywhere.  This would free up your choices of living location significantly and save a lot of money.

Andy

Thanks a lot Andy. Very helpful indications. That is the kind of info I couldnt retrive from google.

Well I will try to make a sort of research in the web to make some possible booking. 

Thanks again