For UK people, try to use a donation place that allows you to mark the donation as Giftaid. I used ActionAid since alphabetically they were the first people I found that had GiftAid, but the Disasters Emergency Committee has this option too:
The Gift Aid scheme is for gifts of money by UK taxpayers. Charities or CASCs take your donation - which is money you've already paid tax on - and reclaim basic rate tax from HM Revenue & Customs (HMRC) on its 'gross' equivalent - the amount before basic rate tax was deducted.
Basic rate tax is 20 per cent, so this means that if you give £10 using Gift Aid, it’s worth £12.50 to the charity
Replies
https://www.donate.bt.com/dec_form_haiti.html
The Gift Aid scheme is for gifts of money by UK taxpayers. Charities or CASCs take your donation - which is money you've already paid tax on - and reclaim basic rate tax from HM Revenue & Customs (HMRC) on its 'gross' equivalent - the amount before basic rate tax was deducted.
Basic rate tax is 20 per cent, so this means that if you give £10 using Gift Aid, it’s worth £12.50 to the charity