It really depends on the area of research you are going into, unless you are applying NSF/NIH/HHMI, all of which require the general GRE (I think). HHMI will pay for the subject if you are applying for a fellowship.
If you know what type of research you will be doing, look for funding in that area. Agencies include american diabetes association, MS society, american cancer assoc., etc. They usually have a lot of info on their websites.
I could be wrong, but if you are funded for MD/PhD, it is difficult to justify to the funding agency that you need their award. Also, some will automatically disqualify you if you have over a certain level of funding. These things are generally all or nothing, and will only allow you to hold one award at any given time. Of course, you can try to get the award "honorary" for your CV.
Trust me, I have tried to max out my grad school $$ as much as possible. Any extra $$ is always useful!! Also, don't overlook smaller, regionalized awards. A few years back, I had a mouse in my cohort that spontaneously developed these bone abnormalities in its extremities. For fun, I tried to breed it, and took some x-rays and histo (mouse xrays can be done with dental facilities 🙂 ). Anyway, there was an arthritis assoc. in my town here that was begging for applications, which consisted of a half page about your potential work. I applied, kind of "why not," and I got $1000! The mouse never amounted to much, except some $$ in my pocket.
Good luck with your applications.
Treg
🙂