Currently have sigma 28-80mm 1:3.5-5.6 and 100-300mm 1:4.5-6.7 lenses both 55mm that I use with my Pentax MZ-50. I would like to purchase a DSLR camera and rather than waste the lenses I already own would like to know if they are compatible with any of the current DSLR models?

I have the same lenses like you, 28-80 come with macro.
I used 28-80 on my pentax k-x dslr without problem, you need to set the apperture on A mode on the lens, otherwise the dslr keep asking about the apperture (F blinking). than everthing is fine.
will tell you later on for the 100-300

Before buying ask the sigma salesman or dealer about it, i know only for nikon camera- it's lenses are compatible for all camera, digital or film base slr cameras.