Mayfield Fund/First Capital Entrepreneurs Helping Entrepreneurs event (great event last night!)
Techcrunch parties
Google Technology Users Group
Startup School
HN meetup (There hasn't been one in a while)
YC/Startup parties (Heyzap, Remail, Vark the past few weeks)
Twitter API meetup
IPhone/Android Meetup
Startup Weekend
Google Campout
Google I/O
and so much more.
Some are paid but all are open to anybody.
TechCrunch parties <- how do I get in on that?
YC/Startup parties <- ditto
Entrepreneurs Helping Entrepreneurs event <- this sounds great, but how did you hear about this?
Lean Startup meetup <- this looks great! I will definitely be at the next one. Thanks. :)
YC/Startup parties: Some people I know RSVPed on Facebook. I also follow several Twitter accounts of YC founders.
Entrepreneurs Helping Entrepreneurs event: Saw it on Techcrunch. I applied and got in.
With regards to meeting seasoned entrepreneurs, just go to events and you'll meet them. Most of them are very generous of their time because they just want to help fellow entrepreneurs.
Just remember though especially with meeting investors that you are one of thousands in the Bay Area that wants a face-time with them.
I haven't really talked to investors. I ask myself why I am worth their time. In my opinion, I haven't done enough to warrant an audience with them. Well, not yet. ;-)