As has been suggested, those mics are not really good enough to get the best out of your recorder (which is capable of making great recordings).
I second the recommendation of Church audio gear. You can see what is available here:
http://taperssection.com/index.php?topic=136212.0For general purpose recordings I prefer cardioids to omnis (unless you can get pretty close to the source and there isn't too much crowd chatter going on).
If it seems a bit more than you want to spend, be aware that it compares to equipment that costs a whole lot more. I hate the cheap Sony mics-they have very poor bass response among other issues.
With most if not all of these mics you will get better performance if you also get a battery box to power them instead of relying on the recorder's plug in power. For acoustic shows you should consider getting a preamp instead of a battery box. If you have to crank up the iRiver's gain too high it will add noise to the recording.
If you got the package that includes CA-14 cards & omnis with the ST-9100, you would be set to make great recordings under almost any conditions.
Again, it may seem like a big investment to you, but if you can swing it you'll be amazed at the results you can get. If you get a mediocre mic and find that you enjoy recording, you'll be replacing it as soon as you can anyway.