That magic $500 mark is a tough point. To be honest, there is only 1 gun under $500 that I like a lot. That's the Stoeger Cougar (can usually be had for about $400 on sale). Move a little over $500 though and there are several I like a lot. For range and home defense a full size is a fine choice and my personal all time favorite the Beretta 92FS is getting close to $500 on sale now. The CZ75B and 75B Compact are also only a little over $500 and they too are great guns. BTW - you'll have to decide on the mechanism you like best ... I prefer hammer guns myself (over strikers) and I like DA/SA trigger actions. Hence the guns I suggested.
I'd definitely go with 9mm, not only is it the cheapest round, it just plain rocks. After trying everything else, I still love 9mm the best of all for everything.
597 VTR, because there's so many cans and so little time!