It depends on what you like in a user interface.
I'd suggest the Pentax Super A/Super Program as it's compact, light, runs from a couple of 1.5v batteries you can find pretty much anywhere and can use any K mount lens which covers full frame. Only downsides are that it uses buttons (rather than a dial) to set the shutter speed in manual mode, and the light meter display tells you how many stops over or under exposure you are (up to three either way) rather than simply indicating the shutter speed you should be using for that aperture setting. You get Program, Shutter Priority, Aperture Priority or Metered Manual modes, the former two only with lenses with an A setting.
I don't regard its being completely battery dependent as a problem. A couple of spares weigh next to nothing and don't cost much, so just keep them in your camera bag.
If you want small, light, with a shutter speed dial and with some sort of automation then look for a P30n or P30t. They cost next to nothing now as collectors are put off by the plastic panels, but the chassis is a solid metal casting so they won't flex or crack. The viewfinder displays all shutter speeds, with one LED showing what you've selected and another flashing to show the speed the light meter recommends. You get metered manual, aperture priority and program mode (the latter only with lenses which have an "A" setting). Battery dependent again but it's hardly difficult to keep spares.
If you're not interested in having multiple AE exposure modes then look for a Pentax MX or KX. The latter is a hefty beast but can handle pretty much anything you throw at it. Shutter speed and aperture are displayed in the viewfinder, the batteries only power the light meter (which uses a match needle display - just align the black needle with the translucent blue one and the exposure is correct). They have no automation whatsoever but are an absolute joy to use.
You could also look for a K2, which can almost be considered a prototype LX.
Anything older may need servicing. My experience is that P30 series bodies and Super As tend to be either perfectly functional or dead, while KXs and MXs usually need new light seals and a clean at least. K2s are much the same, although mine needs to go for some professional attention as the shutter has taken to dragging when held in portrait orientation.
Edit, as someone mentioned the Spotmatic. No, it doesn't need mercury cells or zinc-air. The meter circuit in these is quite happy with modern batteries, although you'll need a spacer to hold them steady in the battery compartment.