I'm 30 (and going to be 31 before the week is over) and I go to an average of somewhere between three and four shows a month.
Most are local shows, but I love live music. Last month I went to Victor Wooten, Solo Bass Night IV, Jackie Greene, and two local shows. And when I was at Berkeley I went/played any show that I my schedule and finances would let me. including pretty much anybody that played at Yoshi's. I figure I've been to between 500 and 600 shows. And if you count festivals (Lollapalooza, Smoking Grooves, Coachella, South by Southwest, Reggae on the River, and now Outside Lands) then I can't even count how many actual bands I've seen.
Some shows that stick out in my mind:
Pearl Jam, Nirvana and Red Hot Chili Peppers on New Year's Eve in 1991. Nirvana killed.
Faith No More, Metallica and Guns & Roses. I left after Faith No More.
Tom Petty at the newly reopened Fillmore in 1997. Incredible (and intimate) venue for a show. I always liked Tom Petty, but he really put on a surprisingly great show.
The Flaming Lips, Hyde Park 2006. I was chaperoning my school's Europe trip and we just happened to have a free day in London during the O2 Festival. Myself, our Italian tour guide, an ex-girlfriend who lives in London and four of my students bought tickets for the day. Unfortunately DJ Shadow and Massive Attack were playing at the same time (we saw Massive Attack) but the Flaming Lips are always a trip to see.
I saw Toots in the Maytals about six years ago in a small club in Sacramento. That was really cool.
While I'm not a huge fan, it was neat to see Norah Jones at Yoshi's before her record was released.
No one else would know them, but seeing criminally underrated (and now defunct) rap duo New Kingdom at a small show in San Francisco in 1998 was awesome.
Off the top of my head those are some that stand out. But I've seen pretty much every band I wanted to live with just a few exceptions.