The particular one I have is a Hayward Goldline AQ-SOL-TC which does have an integrated timer, but also a few other features like temperature sensors that measure pool and solar panel temperatures as well as a digital display. It also has a few operating modes to choose from, like opportunistic heating where if the goal temperature is not reached during timer run time hours it will turn itself on and run if the panel is hotter than the pool, or freeze protection where the pump runs if the outside temperature gets below about 35 degrees. I would describe mine as a mid line model in todays market, although it was probably upper line when it was introduced a few years ago, the most common controller out there is probably the Goldline GL-235, it has been around for years, is simple, and gets the job done, it has a wamer / cooler knob (no temperature display) and interfaces with your existing timer, and a basic on / off / heat / cool selector switch. It is also fairly cheap, selling with a valve actuator (but no compatible valve) for under $200 online if you do a bit of digging (I think I found it for $159 at a couple of places a few months ago).
Ike
p.s. The Pentair Sun-Touch and SolarTouch models are also getting very poplar since being introduced on the market a few years ago, these are a little fancier / more computerized, but not that much more expensive than the Goldline basic models.