This site provides bookmarkable URLs for TfL journeys.
Examples include:
The format is http://tfl.dmi.me.uk/origin/destination/time. Both origin and destination can be either 3-letter station codes, station names, or postcodes. The time argument is optional, and is always in 24-hour format. It represents your departure time unless you add an "a" to the end, which would make it your arrival time.
You can also add options to the end of the URL. By default, it will search for journeys using any method of transport (bus, coach, DLR, rail, river, tram, Tube) but you can change this by adding (transport)=0 as part of the URL. To avoid multiple forms of transport, add each as its own URL segment (e.g. /bus=0/coach=0).