When I went to my RE my OB had allready done the normal RPL panel of bloodwork, but the RE did a ton more (14 viles of blood ... blg!) They also will do a saline ultrasound or HSG (although your regular OB may do this before sending you to an RE) to ensure that the shape of you uterus is okay and there is no scar tissue (endometriosis) They also will take karyotypes and probably a semen analasys from DH, just to make sure that everything is okay there.
For me, he did find a few issues that we are working on fixing, but even more than that, he gave me peace of mind that nothing was getting overlooked. I hope you get one that give you that peace of mind, because it really helps when you are going through all of this! GL