Subcompact 9mm's in the same size/weight category as the PF9:
1. Kahr CW9
PRO: Reliable, stainless, USA-made, great trigger.
CON: Kinda pricey (around $400 new), doesn't take well to sling-shot loading of first round, some issue with spare mags pooping out rounds into your pocket unless you use a snug-fitting holster of some kind.
2. Kahr CM9
PRO: All same as CW9, just a slightly smaller grip (might be a plus for some).
CON: All same as CW9, but slightly smaller grip (might be a minus for some).
3. Smith & Wesson M&P Shield
PRO: Stainless with Melonite finish, USA-made, reliable for most users SO FAR, nice trigger, stainless mags have tapered top end like double-stack mags for easy reloads, manual safety lever.
CON: New design may have early-model bugs, somewhat expensive right now ($400 to $450), manual safety lever, not quite as light or as compact as others in this group.
4. Diamondback DB9
PRO: About the smallest, thinnest, lightest semi-auto 9mm on the market, reasonably priced, available in stainless, Glock-like field strip process, nice trigger.
CON: No last round hold-open, prone to limp-wristing, many reports of hit-or-miss quality control (either it works 100% or it's a lemon), absolutely no +P or 147gr ammo per user's manual.
5. Ruger LC9
PRO: Sort of like a PF9 Version 1.5, slightly more refined production, smoother exterior feel, manual safety.
CON: Poor trigger pull (about 5 lbs. but VERY long), some reports of light primer strikes, manual safety, magazine disconnect safety, goofy loaded chamber indicator.
6. Walther PPS
PRO: Pretty reliable, decent trigger, and ... umm ... yeah. Not sure what else.
CON: Pretty expensive ($500+), weird magazine release, not USA-made, not quite as small as others in same size/weight group.
7. Bersa BP9 Concealed Carry
PRO: Good reliability reports so far, reasonably priced (just under $400), available in stainless (or is it nickel?), comes with 2 magazines, really nice trigger with very short reset.
CON: Not USA-made, new model (may be prone to early-version bugs).
8. Taurus PT709 Slim
PRO: Soft-shooting for its size, nice ergonomics, Glock-like field strip, reasonable price (around $350), available in stainless, comes with 2 magazines, trigger has very short reset (fast follow-up shots), has second-strike trigger capability (reverts to DA trigger on dead primer), manual safety.
CON: Not USA-made, trigger has weird feel (LOTS of slack in SA mode), manual safety, Taurus has very hit-or-miss quality control reputation (either works flawlessly or not at all), not quite as light as others in this category.
9. Rohrbaugh R9
PRO: Pretty much the ultimate in size/weight 9mm specs, supreme fit and finish quality.
CON: INSANELY expensive ($1,000+), so if you ever had to actually use it for defense, your ridiculously expensive pistol goes bye-bye and may never come back (lawsuits, stolen, whatever) ... and, if it eventually does, it's likely to have been knocked around and generally not properly cared for. And anyway, who the heck in their right mind carries a $1,000 pocket-sized 9mm for defense? Sorta like having a $100k pickup truck to use for farm work.
10. Kimber Solo
PRO: Like a miniature 1911, same controls and similar looks, very nice fit/finish.
CON: Excessively expensive ($600+), SA only trigger requires use of manual safety to safely carry Condition One (unlike any of the above pistols), some reports of ammo-picky and limp-wrist-prone pistols.
That's about the only ones equivalent to the PF9 that I know of right off hand. There's also a few double-stack 9mm's by Taurus, Bersa, and others, but that's getting up into a slightly bigger compact 9mm category like the Glock 26 and such.
Hope this helps!