Can anyone point me in the direction of which remotes may or may not work?
If you're looking for compatibility and simplicity, then you really can't beat the original Pentax remote:
Which can be often had for less than $20 USD on eBay: http://www.ebay.com/itm/Genuine-OEM-Pentax-Remote-Control-F-for-Pentax-Camera-/170831571811?pt=Camera_Camcorder_Remotes&hash=item27c65aeb63
And lets not forget the added benefit of having it fit in the K-5 and K-7 grip. Having said that, for the most part... I just use these:
There totally cheap($3 or less), and work fairly well(for short range use). I usually grab a few at a time off eBay and throw them in my bag. The only complaint I'd have with these is that they can they can come with dead batteries. Which isn't much of a problem since the replacements are both common and cheap, and so I buy them in bulk and don't stress over it.
Other than that, if I'm looking for long range, then I use something like this:
I've used both, and they work equally well for long distance shots(quite reliably), though I prefer the low profile version just because the tall one seemed prone to hooking or snagging something along the way.
Hope this helps.
PS. I've used one of the more advanced generic remotes out there on my K20's and found that it was more of a gimick than anything else. These ones are somewhat programmable(shutter speed, intervalometer etc).