Not enough info. How big? A concert xylo? A marching xylo? What's your budget? Whatever you do, it'll probably have to be ordered. I would go to the Woodwind and the Brasswind online store - they seem to specialize in marching and orchestral instruments. Then you have brands - Yamaha, Adams, Ludwig, and I'm sure there are others. I think the website would be www.wwbw.com.
My son just starts learning the xylophone for a middle school band. I hope it can be played as practice and performance. So it should neither be too cheap nor too expensive for the professionals. I do not know what kind of the xylophone is good enough for the beginner performance in the middle school band such as how many notes needed at least, 30, 32 or what else? Can you recommend one?
I don't know what constitutes a "good" xylophone (nor what would make a bad xylo). However, I can tell you that some manufacturers sell beginner percussion packages that consist of a snare (or practice pad) and bells (xylophone). There are a few on this page: http://www.samash.com/drums/student-educational/
The thing is, I see these used on craigslist for cheap all the time.
Basically every one of those beginner bell kits is the same, and that's what you want. There's no real "best" as they're all about the same quality, and will do just fine for a middle school percussionist
I think it needs to be determined from the music teacher what exactly is needed. As mentioned xylophone and bells are often confused. Find out if the bars need to be wooden (or synthetic wood) or made of metal.