I took the GRE back in June and got a 650 on verbal, a 660 on quant, and a 4.5 for the written. My scores more or less mirrored the POWERPREP tools that ETS provided. They are probably the best indicator on how you will perform. All other practice tests I could get my hands on (Kaplan, Baron's, etc.) where either bewilderingly difficult of humorously easy.
My scores are not spectacular, but they're solid and slightly higher than those of the schools that I'm applying to. The verbal in particular. I attribute most of it to Kaplan's flash cards of 500 common words. Many of those words made it into my test.