How to attend conferences without funding I would like to attend some conferences this year, but we are running out of funding until 2015, so I need to look for other options. For instance, I organized a special session in a conference, and attained 12 speakers, so accommodation was free and also registration but not travel expenses. So my question is, if you do not have funding, which other options you know for attending conferences?

P.S. Given my position (PI of a research group), I can not ask for student travel grants, etc
I know your question is based around the assumption that "funding cannot be found" but I write my answer as a challenge to this assumption.

Short answer: Sometimes you can go out and find funding in odd places.

Long anecdote: I was working in a research lab as an undergraduate.  We had very little funds pretty much all the time being in an undergraduate-only institution (with respect to my field of study which is chemistry).  We had some great work that we wanted to take to a fairly prestigious conference halfway across the country but we had no money to go.  Myself and a co-worker knew how much this conference would mean to our boss so we decided to go on a crusade to find money to make this happen.  We marched out of the lab with all pertinent information in hand and took it straight to the top.  We literally walked into the president's office (of the Uni) and asked the secretary if we could meet with him.  She was immediately concerned and amused at what we were trying to do.  Of course we weren't able to see him straightaway, if at all, for our shenanigans.  But she did allow us to make our case to her to see if she could help us out any.  

This turned out to be a very profitable and endearing experience.  She dropped some contacts in various departments and suggested we go talk to them.  She even left us with some business cards to take with us.  We immediately contacted every single person on her list and, much to our surprise, we received some very positive responses.  I remember one office in general, "Undergraduate Enrichment", which dealt directly with the promotion and advancement of undergraduates.  They were nearing the end of the fiscal year and they had money lying around in some accounts that had not been used.  Well, long story short, they gave it to us.  All of it.  We managed to pick up a little bit here, a little bit there, through a few departments, and were able to come up with all the funds we needed.  It wasn't a cakewalk though.  My friend and I went as far as to appear before Student Government where we asked for funds and had to present our case to, for all intents and purposes, a group of dimwits who were not only apart of Greek life, but ran Student Government strictly around the idea of advancing Greek life (i.e. they didn't give two squats about anything we had to say) and it was one of the most painful and grueling 40 minutes of my life standing before them.  We managed to squeak about $500 from them which topped us off.

Summary: My friend and I dove in feet first and asked around for money.  Found the funds in some of the oddest places.  We went on the trip and were able to present our research in a prestigious conference.

Don't give up my friend.  Be proactive and think outside the box. You may walk away being quite surprised.