The ab (Apache benchmark) utility can be used for basic page-level benchmarking:

$ ab -c 2 -n 50 http://localhost/test.php?n=500
This is ApacheBench, Version 1.3d <$Revision: 1.1 $> apache-1.3
Copyright (c) 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Copyright (c) 1998-2002 The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient).....done

Server Software:        Apache/1.3.28
Server Hostname:        localhost
Server Port:            80

Document Path:          /test.php?n=500
Document Length:        6 bytes

Concurrency Level:      2
Time taken for tests:   0.979 seconds
Complete requests:      50
Failed requests:        0
Broken pipe errors:     0
Total transferred:      10353 bytes
HTML transferred:       306 bytes
Requests per second:    51.07 [#/sec] (mean)
Time per request:       39.16 [ms] (mean)
Time per request:       19.58 [ms] (mean, across all concurrent requests)
Transfer rate:          10.58 [Kbytes/sec] received

Connnection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0     0    0.0      0     0
Processing:    18    38   55.4     21   361
Waiting:       18    38   55.4     21   361
Total:         18    38   55.4     21   361

Percentage of the requests served within a certain time (ms)
  50%     21
  66%     37
  75%     39
  80%     39
  90%     49
  95%     83
  98%    222
  99%    361
 100%    361 (last request)