I have recently taken up the Fife in order to play with a local corps. I find that I really like the woodwind experience, but I find it irksome that the fife is not in tune with other instruments. So I have this idea that I would like to simultaneously take up another flute-like instrument in order to be more versatile. But I don’t have a clue how to choose out of the hundreds of choices. I’m sorry if there are other threads that address the same issue, and if so feel free to direct me to them instead of answering the question. I just don’t know what to search to find such a thread. If not, I would like any suggestions, and I bet I get a million different ones. 
you can get a tunable tin whistle, or tunable fife. but the tin whistle is great for beginners to flutes, and starting out on woodwinds.
Ya came to the right place. The whistle is a wonderful little instrument, and many of them are actually in tune with other instruments 
Check out the main part of Chiff and Fipple to get some suggestions on inexpensive instruments for starters. With fife experience, you’ll learn very quickly. Ask any and all questions here: we were all beginners once and are glad to help out.
It sounds like whistles are highly favored. So that’s one option. I have heard a lot also about Irish flutes recently. What is the general opinion of my acquiring a low-cost version of that instrument? Or other ideas too?
Well, if you enjoy fife, then definately buy a whistle (or ten). You can get one for under $10 that will be very playable, and a friend for life.
If you have an interest in checking out the Irish flute, you can do that for under $100 also. The most popular entry-point around here, and a fine player in its own right, is the PVC (plastic) flute made by Doug Tipple. He’s a frequent poster, great guy, and makes a nice, playable flute. Do a search, and you’ll find lots of praise. His site is at:
http://dougsflutes.googlepages.com/home
…would be, here on the whistle forum, eh?
there is a flute forum… 
..would be, here on the whistle forum, eh?
lol, whoops 
I somehow took the first topic on the main page and assumed it was sort of generic etc. Sorry about that little oversight. That being the case, I’ll ask a different question: if I do choose a whistle as another instrument, how do I choose one that will sound good in ensemble with other instruments, (i.e. guitar)?
Edit: also, thank you to crookedtune for the link. I started fife on a pvc instrument. I know they can certainly be of unexpected quality. Do you have a link for those whistles? I think I would definitely buy such an instrument.