Hey guys just thought i'd contribute my 2 cents given that I ride every other day road and mountain

For the girl I'd definitely recommend looking into 2 brands that specifically focus on women's design since women's bodies are anatomically different from males Specialized and TREK both have WSD (Women Specific Designs) and they have some good road bikes. There are a few other brands out there but I think everyone out there will agree that the best entry level road bike is the Specialized Allez. Trek makes some good WSD bikes too but dealers around where I live price'em a little higher.

As for the mountain...There's a bunch of good MTB bikes out there, but not much for $500 range. I think the best bang for the buck is probably the hardtail Specialized Rockhopper (good frame) or the Norco Charger/Storm.

It really all depends on what you ride...if you ride together, there's no way I'd take that road bike on a trail ride...you'll end up destroying your bike. And if you're S/O rides the road with his MTB you'll blow by him in no time because of your road bike design. You could get a tandem bike Those are always fun