Can anyone list classic blues ballads that has a great rythm progression that should be in everyone's repertois?

Jimi Hendrix songs are great because they integrate riffs with rhythm.  I am looking for some great classic blues song to learn and play.  Songs that have great riffs ingrated with rhythm.  Something that is probably 12 bar based and will give a little room to do some pentatonic improvs...;)

Thanks for your suggestions.