Ear protection should be considered mandatory above certain levels.......or if you play with a loud drummer, that is! :-D
I use these earplugs at rehearsals, they offer good protection while still letting through a "usable" sound (i.e., they don't cut off certain frequencies, just make the sound less loud, allowing you to hear what you're playing and/or singing though, it has to be said, if you're mainly a singer, a pair of in-ear monitors would be more suitable).
I find them quite comfortable, I usually wear them for about two hours, sometimes even more so, without any strain on my ears.
They're washable and they're cheap; do yourself a favour.