I personally would love to be able to donate more to open source (specifically Postgres and some of its related projects) but I haven't found a way yet which meets my few simple criteria.
* The money has to specifically go to developers or development and testing related costs, not general advocacy or evangelism.
* It would be nice if donations could go into specific pools, eg in the Postgres example, I might be interested in contributing funds for performance enhancements but have no interest in logical replication.
* Variety of payment methods supported, with annual, repeating donations allowed.
Bountysource (https://www.bountysource.com) comes close, but rarely has many projects for funding.
Its surprising that in 2014, one of the best ways to supporting open source is still to select a company which does work on your favourite OSS project and buy a support contract or something, even though it's not a very efficient way.