Please find below some commands and utilities which can help you working and monitoring Apache server. More stuff will be added once I discover it.

Monitor your website in real time with apachetop:
This tool is very interesting, it lets you view exactly what is happening, displaying data like requests per second or total bytes. It is parsing the apache logfiles and displaying meaningful output to the screen.

How to use it? Simple:
jupiter:~# apachetop -r 1 -f /var/log/apache2/sites/docs.gz.ro.log

The display will look similar to this one:

last hit: 19:29:06         atop runtime:  0 days, 00:01:25             19:29:15
All:           36 reqs (   0.6/sec)       1198.1K (   19.0K/sec)      33.3K/req
2xx:      36 ( 100%) 3xx:       0 ( 0.0%) 4xx:     0 ( 0.0%) 5xx:     0 ( 0.0%)
R ( 30s):      19 reqs (   0.6/sec)        548.8K (   18.3K/sec)      28.9K/req
2xx:      19 ( 100%) 3xx:       0 ( 0.0%) 4xx:     0 ( 0.0%) 5xx:     0 ( 0.0%)

 REQS REQ/S    KB KB/S URL
    8  0.80 259.1 25.9*/node/29
    2  0.07  60.4  2.2 /osx
    2  0.08  72.3  3.0 /node/60
    2  0.11  59.9  3.2 /node/70
    1  0.05  48.0  2.2 /osx-lion-diskutil-encrypt-decrypt-hfs.html
    1  0.08  39.9  3.1 /tips-and-tricks

You can find more tricks about this tool, here: http://www.howtogeek.com/howto/ubuntu/monitor-your-website-in-real-time-with-apachetop/

Using ab benchmark tool.
This tool is very interesting, you can test your web server's settings. There are various options and you can find them by reading the command's manual but I will show you now just two:
-n 100: ab will send 100 number of requests to server http://docs.gz.ro/;
-c 2: 22 is concurrency number, meaning it will send 2 requests in the same time to the target.
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Example:

core:html# ab -n 100 -c 2 http://docs.gz.ro/
This is ApacheBench, Version 2.3 <$Revision: 655654 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking docs.gz.ro (be patient).....done


Server Software:        Apache/2.2.16
Server Hostname:        docs.gz.ro
Server Port:            80

Document Path:          /
Document Length:        27703 bytes

Concurrency Level:      2
Time taken for tests:   21.685 seconds
Complete requests:      100
Failed requests:        0
Write errors:           0
Total transferred:      2819800 bytes
HTML transferred:       2770300 bytes
Requests per second:    4.61 [#/sec] (mean)
Time per request:       433.694 [ms] (mean)
Time per request:       216.847 [ms] (mean, across all concurrent requests)
Transfer rate:          126.99 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.2      0       1
Processing:   333  433  56.6    426     641
Waiting:      306  406  53.9    399     617
Total:        333  433  56.7    426     642

Percentage of the requests served within a certain time (ms)
  50%    426
  66%    450
  75%    464
  80%    473
  90%    494
  95%    545
  98%    641
  99%    642
 100%    642 (longest request)

How to check which pages are hot-linking your images from the apache log? Below, with awk we use " as separator, search for image extensions and exclude our url. Finally we sort the output and count the duplicates:

jupiter:~# awk -F\" '($2 ~ /\.(jpg|gif|png)/ && $4 !~ /mediashow\.ro/){print $4}' /var/log/apache2/sites/mediashow.ro.log | sort | uniq -c | sort -n

How to dynamically display only hot-linked images, excluding your domain and empty referrers:

jupiter:~# tail -f /var/log/apache2/sites/mediashow.ro.log | awk -F\" '($2 ~ /\.(jpg|gif|png)/ && $4 !~ /(mediashow\.ro|-)/){print}'