For the rear, make sure the number of speeds is right. Most are 9 but there are still some 8 speed stuff out there. (I wish they would bring back 8 speeds!) Most of this is in the shifters having an extra click but I have seen a few 8 spd rear deraileurs not able to go the extra little bit.
For the front, newer stuff works with everything but the size of the seat tube and whether its a top pull (cable comes from the top) or a bottom pull (cable comes from the bottom under the BB).
For value and performance Shimano LX is actually pretty good. Sram makes good stuff but usually it's a little more expensive depending on what you get.
What's a derailer? I usually look for bikes with only one gear, less hassle of tuning, maintenance, etc. Really though, I still ride 8 speed stuff on my F/S bike and usually stick with Shimano LX or better and haven't had any problems.
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