When you ask this question, you are asking two questions; what software and what hardware (prompter head).
I find almost all heads out there ridiculously overpriced. I bought a head from Stewart instruments and as very pleased. I thought it every bit as good as a Q-Tv for half the price. It has more than paid for itself. It IS a CRT-based head, which has pros and cons. Most folks today would probably go with an LCD-based head. Stewart may offer those now as well, you'd have to check. They are the ones that advertise the "ridiculously low-priced prompters". In the back of TV Technology magazine. They bundle some prompting software with most heads, it's just OK IMO.
For mac based prompting software, I'm not sure, not up on the latest choices. For PC I HIGHLY recommend DRS-Digitrax's stuff. WAY cheaper than Q-TV or similar, no annoying dongles, works on anything from a 486 to modern laptop, easy to use plus extra features. Free working ownload to evaluate, if you like it (you WILL) they email you an unlock code to make the nag screens go away.