We actually provide a full, branded website for nonprofits. Most everything is baked in for them - blog, automatic receipts for donations, etc. WePay is a great service but they don't provide websites - they handle transactions. We use do use WePay's API to handle the transactions on the nonprofits' websites.

First Giving is a great service as well but if I understand their model correctly, it is more of a fundraising page for an individual to raise money for a nonprofit.