I'm looking for a model that retails for under $500 brand-new (or quite a bit less used) - reliability is more important than high pressure or flow rate.

Looks like Ex-Cel/DeVilbiss/Porter-Cable, Generac and Karcher make their own pump heads, everyone else seems to install a generic model. The few online opinions seem to run the whole gamut - some folks love a particular brand, others have horror stories to tell (leaking pump seals, blown pump housings, not-so-reliable Honda engines, etc.).

Anyone have a model that they love (or hate)?

I bought a Ex-Cel or DeVilbiss from Home Depot. Think it work for 3 years ,light use, then the pump went out. The last year the pump was sticking. Took the pump apart and a couple screws broke.  I wouldn't buy another cheap HD presser washers again.

I bought a Karcher used, from a neighbor two years ago for $150.00. It works really well and it's been reliable, except for the ruptured gas tank, which was  Briggs and Stratton's fault. The crappy plactic tank split at the seam but B&S replaced it free. There had been a recall that I found out about when I went to the small engine repair shop to buy the new tank.

tagged for reference

(because the one I bought at Sears is a worthless POS)

Learn how to rebuild them.

 Even the best industrial ones quit pumping.

I'm not sure where to start on rebuilding them. I went to home depot and looked for a "rebuild your old pressure washer" book but couldn't fine one

are they really complicated?

Quoted: are they really complicated?

Nope. Most of what you need to know should be in the owners manual. (parts list, ect)

Mostly piston seals,packings,check valves.

I'm not sure that some of the cheapies are even designed to be rebuilt. Not much point in using a 'throwaway' engine if you're not going to also use a 'throwaway' pump...

I talked to a fellow at Cam-Spray (maker of high-end models for industrial applications) who says that some of the cheapest pumps aren't good for more than approximately 50 hours – and that's assuming nothing breaks prematurely.

One last bump for the Night Crew...