If you are otherwise pleased with your E-500, a good fast lens for it would be over $1000:
http://www.amazon.com/Olympus-50-200mm-2-8-3-5-Digital-Cameras/dp/B000X1P5RE
A new camera will have much better high ISO performance, enough that it coupled with a modest lens might work just as well as your Oly with the above fast glass. A newer camera will have other performance benefits as well in terms of auto-focus and cycle times. Here is one of the best budget low-light shooters:
http://www.amazon.com/gp/product/B004V4IWKG/ref=s9_simh_gw_p23_d0_g23_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=1R6Q4GZ705SWHE51CJCX&pf_rd_t=101&pf_rd_p=470938631&pf_rd_i=507846
A "cheap" fast telephoto lens for the Nikon:
http://www.amazon.com/Sigma-70-200mm-Macro-Digital-Cameras/dp/B001044RIQ/ref=sr_1_2?s=electronics&ie=UTF8&qid=1316192560&sr=1-2
I have an Olympus E500, but may need to upgrade to a new body and/or lens. Any suggestions? I am not opposed to getting used... I don't need the best of the best.
I want to shoot better action shots during low-light situations (without a flash if possible). Do I need a new camera altogether... or do I need to invest in a better lens... or both?
Primary uses for low-light: evening football & indoor basketball (sports in general)

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