Panasonic Lumix G 20mm f/1.7 pancake
This lens does not come with a hood at all. While a hood is probably not much needed from a stray light perspective, I still like to put a hood on my lenses for protection against objects accidentally touching the front lens element.
My favourite solution is to put a 46mm to 37mm step down ring as hood. This gives some basic protection of the front lens element, while keeping the overall package compact.
I've checked that there is no extra vignetting caused by the step-down ring.
In addition, you'll need a 37mm front lens cap. Both can be gotten from various auction sites for about US$10 in total.
This lens features a traditional focus mechanism, in which the whole lens assembly moves back and forth. Adding extra weight to this assembly is generally not a good idea. However, the step-down ring doesn't add that much weight. Less than a glass filter would, anyway.
Another solution is to get a 46mm metal screw in hood designed for Leica Summicron:
While this hood looks stylish, I think it adds too much bulk. Besides, you might not be able to fit the front lens cap inside it.
Panasonic Leica Lumix DG 45mm f/2.8 1:1 macro
This lens does come with a hood, however, I am sad to say that I find the hood completely hideous:
This hood does look stylish, and reminds me of the older Leica hoods. However, it is much too wide, and could have been used for a wide angle lens. But this lens is a short tele. So the hood does not do a good job of keeping stray light out.
I prefer a hood that is a narrow as possible, while still not inducing any extra vignetting. I found the solution I like by adding three extra elements to the front lens thread: First a 46mm stand off ring (glassless filter), then a 46mm-37mm step-down ring, and finally, a 37mm-28mm step-down ring:
I was almost a bit surprised when I verified that this combination does not add any extra vignetting. But the front lens element of the 45mm macro has a rather narrow diameter, so I suppose it makes sense.
This "hood" does not add any extra diameter to the lens, which is good. In addition, you'll need a 28mm front lens cap. Such a cap is pretty inexpensive.
Olympus M.Zuiko Digital 45mm f/1.8
In a move which has annoyed quite some fans, this lens is not sold with a hood included. There is a hood you can buy from Olympus, which fits in to the bayonet mount. However, it is quite expensive.
I bought a collapsible rubber hood for screwing into the 37mm front threads. It works great:
This rubber hood cost me US$13, including shipment from China.
Panasonic Lumix G 14mm f/2.5 pancake
Just like the 20mm pancake, this lens does not come with a hood. Again, I've used the same solution as with the 20mm pancake lens: A 46mm to 37mm step down ring as hood:
In this case, I had bought a grey ring by a mistake, so I had to paint it black with enamel paint. No big deal.
This lens features internal focusing, so I am not afraid of putting some extra stuff onto the front lens thread.
Panasonic Lumix G 45-200mm f/4-5.6 Mega O.I.S.
This lens does come with a hood, and I think the hood is very well designed:
The only problem I can see, is that it is awkward to insert and remove the front lens cap.
I still changed this hood, since it was a tad bit too long for my camera bag. I got a 52mm screw in metal hood:
This alternative hood is probably not as good for protection, but is is more practical to use, and it's easier to add the front lens cap after use.
The kit zoom lenses generally have well designed hoods, and I see no reason to replace them.