Though competition's increasing for low-end full-frame cameras, the Nikon D610 holds its own; that said, while slightly faster than its predecessor it's not a whole lot different.
The Nikon D600 is a really good camera for the money, as long as you're willing to shell out for the lenses that can do it justice.
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Versatile, sturdy, and built with high-quality optics, the Sigma APO 70-200mm F2.8 EX DG OS HSM offers a good value, although it's not exactly cheap.
A fast, inexpensive dSLR with better-than-average low-light quality, the Pentax K-x nevertheless has some flaws, such as unreliable image stabilization, to watch out for.
The Nikon D300s is a great camera, especially if you need the burst speed or slightly improved low-light focus, but if you don't care about video you might consider looking for a really good deal on a D300 and using what you save to splurge on a good lens.