Below are some useful links for dealing with depression and suicidal thoughts.
This list is mostly UK centric but also includes some links for international readers. Feel free to add your own suggestions in the comments section.
NHS - Help for suicidal thoughts
International Bipolar Foundation - List of International Suicide Hotlines
CALM - Campaign Against Living Miserably
Students Against Depression
Suicide Prevention Line (USA)
Beyond Blue (Australia)
Depression.org.nz (New Zealand)
South African Depression & Anxiety Group