Memory Problems

I have a system running RH 7.3. I have recently been concerned about my
server running out of memory. I added 1GB of memory to my server to see if
by chance 256 isn't enough. When I first boot up my server the free memory
is 185324. A run of free a day later gives me the following output:

             total       used       free     shared    buffers     cached
Mem:       1289408     661136     628272          0      13624     515040
-/+ buffers/cache:     132472    1156936
Swap:      2359208        792    2358416

I tried stopping every process individually to find what is taking all of
the memory. The most I went down was around 10K. Is there any programs that
will tell me all segments of memory and what program is in it. I have tried
using top but it only shows me 15 or so pids. Also what is the cached that
free shows. If this is a kernel thing is there a place where I can place
what the maximum cache should be or how to clear it.

Thanks,

Ben