I just put my 1.75"s on last weekend. Unbelievable difference in sound, I love 'em.
Got 'em from American Classic Motorcycles on e-bay for $250 including shipping.
Great investment, easy to install, nothing else to do but ride once you get them on.

 

I had the 1.75" Rush black slip-ons on the Nightster in my sig pic. They were fantastic (low rumble with no drone or raspiness), in fact, the best mod I did to that bike -- even better than the HD black fwd controls, which were also awesome.

-But on my '07 Street Bob, I was (and am) still disappointed. The Nightster sounded much, much deeper/lower and better than my Dyna, which I think is ridiculous. Also, I had absolutely zero popping on the Nightster with the Rush 1.75" (the Nightster actually ran much better with them than with the stock exhaust). The Dyna was popping on deceleration with its Rush 1.75" slip-ons until I got the XIEDs.

-Just my $0.02. Again, I bought the Rush slip-ons with 1.75 baffles for my Dyna solely because I was so impressed with them on my Nightster. I'm not happy with the result, but your results may vary! For me, I'll probably try a bigger baffle, and then try Thunderheaders if I still don't get the low rumble I'm after.