I found  physics.stackexchange a very instereting place. It is a place that you can ask physics questions and some one will answer them.

Some questions that look simple actually touch some deep issues.
Some  questions can motivate research projects.

Here are some samples:

What does it mean for a Hamiltonian or system to be gapped or gapless?

Gauge symmetry is not a symmetry?

What is spontaneous symmetry breaking in QUANTUM systems?

How to understand the emergent special relativity in the superfluid?

Are elementary particles actually more elementary than quasiparticles in condensed matter physics?

Having a lot of questions and being able to ask good questions is a key to do good research.

A physics/math student should learn how to ask questions; the questions that are beyond how to solve homework problems. So, do you have a question (when you are not doing homework)?

Here is a list of my answers to some of the questions that I found interesting.
Here is a list of the questions that I found interesting.

The math site http://mathoverflow.net/ is more impressive (much better than the above physics site).

When I have a real math question in my research (I mean a real math question), I just ask
http://mathoverflow.net/. I will get an answer within one day, and include the answer in my paper (with a quote to http://mathoverflow.net/).

Here is a list of the math questions that I asked.

Here is a list of the math questions that I found interesting.

From those questions, you may also gain a feel about where is the frontier of the current research.