Yum install php-pecl-memcached - No package found (Have epel-release-6-8.noarch.rpm)

You have almost certainly mistakenly excluded some packages with yum's exclude option in your yum.conf or a file which it includes. For instance you may have:

exclude=php*

This would prevent any package whose name begins with PHP from ever being shown to you.

To fix the problem, remove the exclusion from your yum configuration.

(This was probably done as a misguided attempt to version-lock the PHP packages. Use the yum versionlock plugin to accomplish this instead.)

Expanding on @Michael Hamptons answer. You could have debugged this issue like this as well.

1. First confirm same system as OP

% uname -a
Linux data01 2.6.32-279.14.1.el6.x86_64 #1 SMP Tue Nov 6 23:43:09 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
% cat /etc/redhat-release 
CentOS release 6.3 (Final)

2. Show yum cmds when there is no exclude=php* present in /etc/yum.conf

% repoquery *pecl* --location
http://eq-centosrepo.hopto.org/6.3/os/x86_64/Packages/php-pecl-apc-3.1.9-2.el6.x86_64.rpm
http://eq-centosrepo.hopto.org/6.3/os/x86_64/Packages/php-pecl-apc-devel-3.1.9-2.el6.x86_64.rpm
http://eq-centosrepo.hopto.org/6.3/os/x86_64/Packages/php-pecl-memcache-3.0.5-4.el6.x86_64.rpm

3. Show repos

% yum repolist
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
 * base: yum.singlehop.com
 * extras: mirror.anl.gov
 * updates: mirrors.seas.harvard.edu
repo id                                                  repo name                                                            status
base                                                     CentOS-6 - Base                                                      6,346
extras                                                   CentOS-6 - Extras                                                       17
updates                                                  CentOS-6 - Updates                                                   1,048
repolist: 7,411

4. Add an exclude=php* to /etc/yum.conf

% vim /etc/yum.conf
...
...
exclude=php*
...

5. Confirm php* packages are excluded

# with repoquery

% repoquery *pecl* --location
% 

# with yum

% yum list all php-pecl*
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
 * base: yum.singlehop.com
 * extras: mirror.anl.gov
 * updates: mirrors.seas.harvard.edu
Error: No matching Packages to list

6. Tell yum to ignore the excludes using --disableexcludes=all switch

% yum list all php-pecl* --disableexcludes=all
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
 * base: yum.singlehop.com
 * extras: mirror.anl.gov
 * updates: mirrors.seas.harvard.edu
Available Packages
php-pecl-apc.x86_64                                                    3.1.9-2.el6                                              base
php-pecl-apc-devel.x86_64                                              3.1.9-2.el6                                              base
php-pecl-memcache.x86_64                                               3.0.5-4.el6                                              base