Power Factor Pro, in particular, this newer model, is excellent.
I have a PL Plus DMC in my 3-space rack, and it's just fine.
A lot of the time, now that using an AX8, I just use my older Power Factor Pro without any issue.
What I would like though is something that regulates voltage, with the same features as the new Power Factor Pro. I believe there is a Furman unit like that, but I forget which.
A good UPS is also something I've considered, but I would prefer to take a rack version, and they're more expensive. I actually use a UPS at home, along with the PL Plus.