Canon Rebel T3 or Nikon equivalent. Nothing wrong with Sony or Pentax, just not enough compatible gear that's available on the new or used market in my opinion. I suggested an entry level camera to you for three reasons.
1) You posted in the beginner's section so I assume you're a beginner. If that's true, you'll just be wasting shutter life on anything else while you're learning all about it.
2) If you have to ask, go with the most inexpensive body of the brand you want. I say that because a camera is a tool. They don't just get better and better as the price goes up. Do you need a full frame? Do you need 1/8000 shutter speed? Maybe you'd actually be better off with a cropped sensor. Do you need 3 fps or 7? If you honestly don't know the answers to those questions, get an inexpensive body, and then when you figure out what you need it'll be time to upgrade anyways.
3) You listed a budget. For anyone starting out with a budget under $50,000 USD I always suggest go with the inexpensive body and use the rest for top quality glass, flashes, grips, remotes, tripods, filters, gels, cases, bags, etc. With $2,500 you can get a 5D Mk II and one two "ok" lenses. Or you can get a Rebel T3, 580 EXII, battery grip, extra battery, 18-200mm walk around lens, 85mm f/1.8, an off brand 28-70mm f/2.8 and an off brand 70-200 f/2.8 and a nice case or bag for all of it. Just as an example.