When looking for what can be uninstalled to reclaim space:

rpm -q -a --qf "%10{SIZE}\t%{NAME}\n" | sort -k1,1n  

Sample output:

 51721748    boost-devel
 57180821    wireshark
 65074768    libgcj
 71492413    db4-devel
 79152667    valgrind
 85414200    java-1.6.0-openjdk
108920679    kernel  
112425302    glibc-common  
115976633    squeezeboxserver  
116424867    kernel  
116467238    kernel  
204226588    fluid-soundfont-lite-patches  

Decide what's safe to remove and the perform a yum remove to see what dependencies will get removed along the way before deciding if it can really be uninstalled.