Since Linux-VServer is a community project, so 'donating' some time, cleaning up wiki pages or adding new documentation, adapting other kernel patches to work with vserver, contributing to vserver development, or 'just' testing vserver in production-like environments, can be very useful to vserver evolution.
For more information take a look at How to participate
Good development resources are scarce, and sometimes such a simple thing like additional memory or harddisk space might help a lot. Access to unusual hardware, for kernel and userspace testing, or unused equipment is another thing which will be useful, and appreciated.
VServer developers often pay a lot to have access to the internet or to host their development or web servers, therefore providing connectivity, hosting or development space could help.
Note: CreditCard Payment in US$: 3.9% + $0.30 go to PayPal :(