To finance game-servers and webspace for fora, homepage, repositories etc. i suggest to think about flattr. It's starting off at the moment as uncomplicated micro-donation method to support blogs mostly, but there are no restrictions on the type of project to be financed.
It has several advantages to other payment services like paypal, the most important is that it is very much unlike paypal. Inedpendent (the profit doesn't go to one of the really bad companies like ebay) it is based in Sweden (seated in the US is a very big deterrant due to the non-existent privacy).
Right now flattr is the most widespread in german speaking countries, netizens there adopted it quite fast. (Perhaps because germans who read blogs are usually more tech savvy and concerned about net-culture than us blog readers. Simply because a much broader slice of us society reads blogs while, to overgeneralize, only german nerds do so.)
This is however an advantage for simutrans, due to beeing rooted deeply in the open source community and having a large portion of german users and devs.
Unlike pay-pal, as an example, flattr users already planed to donate a certain amount of money every month. Clicking flattr buttons will just change the distribution of this money, this causes the stream of money from a single user to be much smaller, but also much more regular. The monthly work to do so is just pressing one button.
You can read about flattr on wikipedia (http://en.wikipedia.org/wiki/Flattr), a video (http://youtu.be/kwvExIWf_Uc) and it's homepage (http://flattr.com/).
Interesting alternative to paypal. We should consider it.
PS: By fora you meant forum, right? :P