The 
free command show the free amount of memory in megabytes. Changing the "
m" to "k" or   "
g" gives the output in kilobytes or gigabytes respectively. Just "
free" gives the output in bytes I think.
The free amount looks surprisingly small. Because it includes the amount used as cache and buffers. But it's not serious. For reasons we've beaten to death in every "My phone ate my RAM HELP!!!" thread.
I think there's a glitch that doesn't list the cache amount in Android. But you can run it on your Linux machine to see how it's suppose to look. 
Mine looks something like this for my computer:
	
	
	
		Code:
	
	
		free -m
             total       used       free     shared    buffers     cached
Mem:          7371       5243       2128          0        223       2160
-/+ buffers/cache:       2859       4512
Swap:         4124          0       4124
	 
 
For my phone:
	
	
	
		Code:
	
	
		free -m
             total       used      free    shared    buffers   
Mem:          793          742       51         0        17      
-/+ buffers:               725       68
Swap:         499           92      407
	 
 So out of my 1Gb of RAM, I can use 793MB. I've used 742MB and only have 51MB completely free. However, my task manager reports 444MB used and 348MB free. I must assume that it doesn't count the amount used by cache and buffers. Other than Android Terminal Emulator, no apps are reported by my task manager either. 
 
Because task killers only kill applications, the amount cleared could be potentially small. You could clear all your apps, but RAM could still remain almost full due to cache and buffers. So a phone may become responsive after killing apps, but not necessarily because you freed a few megabytes. 
The 
top command gives a similar output. It also shows application information too. Give these commands a try.