When I performed my initial install, I was not able to install ANY of the recommended plugins.  After install, when I try to "correct" them (from Manage Jenkins link), they all fail and I get a 503 error:

java.io.IOException: Server returned HTTP response code: 503 for URL: http://mirror.xmission.com/jenkins/plugins/trilead-api/1.0.5/trilead-api.hpi
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1900)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1498)
at sun.net.www.protocol.http.HttpURLConnection.getHeaderField(HttpURLConnection.java:3061)
at java.net.URLConnection.getHeaderFieldLong(URLConnection.java:629)
at java.net.URLConnection.getContentLengthLong(URLConnection.java:501)
at java.net.URLConnection.getContentLength(URLConnection.java:485)
at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:1194)
Caused: java.io.IOException: Server returned HTTP response code: 503 for URL: http://mirror.xmission.com/jenkins/plugins/trilead-api/1.0.5/trilead-api.hpi
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at sun.net.www.protocol.http.HttpURLConnection$10.run(HttpURLConnection.java:1950)
at sun.net.www.protocol.http.HttpURLConnection$10.run(HttpURLConnection.java:1945)
at java.security.AccessController.doPrivileged(Native Method)
at sun.net.www.protocol.http.HttpURLConnection.getChainedException(HttpURLConnection.java:1944)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1514)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1498)
at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:1210)
Caused: java.io.IOException: Failed to load http://updates.jenkins-ci.org/download/plugins/trilead-api/1.0.5/trilead-api.hpi to /var/lib/jenkins/plugins/trilead-api.jpi.tmp
at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:1217)
Caused: java.io.IOException: Failed to download from http://updates.jenkins-ci.org/download/plugins/trilead-api/1.0.5/trilead-api.hpi (redirected to: http://mirror.xmission.com/jenkins/plugins/trilead-api/1.0.5/trilead-api.hpi)
at hudson.model.UpdateCenter$UpdateCenterConfiguration.download(UpdateCenter.java:1251)
at hudson.model.UpdateCenter$DownloadJob._run(UpdateCenter.java:1799)
at hudson.model.UpdateCenter$InstallationJob._run(UpdateCenter.java:2070)
at hudson.model.UpdateCenter$DownloadJob.run(UpdateCenter.java:1773)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at hudson.remoting.AtmostOneThreadExecutor$Worker.run(AtmostOneThreadExecutor.java:111)
at java.lang.Thread.run(Thread.java:748)