I'm still waiting on the other two, but i'll have a total of three Zoom H1's and still my Zoom H4n. I have ordered more Audio-Technica ATR3350 Lav microphones which is a Mono mic (not stereo), and if you're looking into those cheaper shotgun microphones, those would be mono as well. If you're lucky they might already adapt to record in two channels like the Rode Videomic does. Since the ATR3350 Lav mic and possibly some of these other mono microphones records only to one side channel of the Zoom Audio recorder, to save yourself some time duplicating audio tracks in post, you can grab one of these mono-to-stereo adapters. (make sure it's mono to stereo not vice versa) The correct size you'll need is 3.5mm (a.k.a 1/8"). Here's the link to a Mono to Stereo Adapters on eBay.
Another interesting comment that came in suggested the use of a Dual input adapter. This may work to input two mono microphones one for each channel. The Zoom H4n can record 4 channels, two of them mono which needs to be duplicated to both left and right channel in post. Using a Dual input adapter, you might be able to achieve the same thing with the Zoom H1. You may have to depend on using self powered microphones, and also you won't be able to adjust individual levels like the Zoom H4. Curious if that idea would work.