The original post only has US helplines. I've added UK helplines underneath. It would be great if people could add numbers from everywhere in the world.
Depression Hotline 1-630-482-9696
Suicide Hotline 1-800-784-8433
LifeLine 1-800-273-8255
Trevor Project 1-866-488-7386
Sexuality Support 1-800-246-7743
Eating Disorders Hotline 1-847-831-3438
Rape and Sexual Assault 1-800-656-4673
Grief Support 1-650-321-5272
Runaway 1-800-843-5200, 1-800-843-5678, 1-800-621-4000
Exhale After Abortion Hotline/Pro-Voice: 1-866-4394253
Child Abuse 1-800-422-4453
UK Helplines
Samaritans (for any problem) 08457909090 e-mail jo@samaritans.org
Childline (for anyone under 18 with any problem) 08001111
Mind infoline (mental health information) 0300 123 3393 e-mail: info@mind.org.uk
Mind legal advice (for people who need mental-health related legal advice) 0300 466 6463 legal@mind.org.uk
b-eat eating disorder support 0845 634 14 14 (only open Mon-Fri 10.30am-8.30pm and Saturday 1pm-4.30pm) e-mail: help@b-eat.co.uk
b-eat youthline (for under 25's with eating disorders) 08456347650 (open Mon-Fri 4.30pm - 8.30pm, Saturday 1pm-4.30pm)
Cruse Bereavement Care 08444779400 e-mail: helpline@cruse.org.uk
Frank (information and advice on drugs) 0800776600
Drinkline 0800 9178282
Rape Crisis England & Wales 0808 802 9999 1(open 2 - 2.30pm 7 - 9.30pm) e-mail info@rapecrisis.org.uk
Rape Crisis Scotland 08088 01 03 02 every day, 6pm to midnight
India Self Harm Hotline 00 08001006614
India Suicide Helpline 022-27546669
Kids Help Phone (Canada) 1-800-668-6868, Free and available 24/7
suicide hotlines;
Argentina 54-0223-493-0430
Australia 13-11-14
Austria 01-713-3374
Barbados 429-9999
Belgium 106
Botswana 391-1270
Brazil 21-233-9191
Canada 1-800-448-3000
China 852-2382-0000
(Hong Kong 2389-2222)
Costa Rica 606-253-5439
Croatia 01-4833-888
Cyprus 357-77-77-72-67
Czech Republic 222-580-697, 476-701-908
Denmark 70-201-201
Egypt 762-1602
Estonia 6-558-088
Finland 040-5032199
France 01-45-39-4000
Germany 0800-181-0721
Greece 1018
Guatemala 502-234-1239
Holland 0900-0767
Honduras 504-237-3623
Hungary 06-80-820-111
Iceland 44-0-8457-90-90-90
Israel 09-8892333
Italy 06-705-4444
Japan 3-5286-9090
Latvia 6722-2922, 2772-2292
Malaysia 03-756-8144
(Singapore 1-800-221-4444)
Mexico 525-510-2550
Netherlands 0900-0767
New Zealand 4-473-9739
New Guinea 675-326-0011
Nicaragua 505-268-6171
Norway 47-815-33-300
Philippines 02-896-9191
Poland 52-70-000
Portugal 239-72-10-10
Russia 8-20-222-82-10
Spain 91-459-00-50
South Africa 0861-322-322
South Korea 2-715-8600
Sweden 031-711-2400
Switzerland 143
Taiwan 0800-788-995
Thailand 02-249-9977
Trinidad and Tobago 868-645-2800
Ukraine 0487-327715