How can I fund my PhD after the first year?
In the US, various funding agencies (NSF, NIH, DOE, ...) have fellowships you can apply to for predoctoral students. They tend to be very competitive compared to internal sources (Teaching Assistantships, Research Assistantships, Graduate Assistantships), but they may offer a higher stipend.

Depending on your field, professional societies also offer fellowships: American heart association, Whitaker foundation, Gates foundation.

Industry also offers some in association with various schools: Siemens, Raytheon, Johnson &amp; Johnson.