I am not sure contributing with money is the best way to help OpenSource software. When Jeff Atwood gave some $5000 to an OpenSource project the lead of the project was grateful... but if I recall correctly he was not too sure about what to do with it.
Developers who contribute to OpenSource projects are not paid to do so. They do it because they like it, want to prove something to themselves, etc... but money is never the cause since they know that they won't probably earn a dime. At best, they might attract attention which may then generate revenues (think new employer, more traffic to their blog, etc...)
Now, I don't say that one should not contribute, but I think that monetary contributions are not as efficient as one might think, companies have a tendency to think that their model (capitalist) naturally extend to everything around them :/
In my opinion, an OpenSource project benefit more from patches/bug reports than from direct monetary contribution, exceptions being hosting the website / repository of the project or financing meetings for the top contributors so that they can discuss face to face when the need arise, but though this cost money, this is not directly giving money.