I'd like to post a design I'm working on to get some feedback and suggestions from the community. Is this site a good place or are there other better suited sites?
One useful site is FiveSecondTest.
It's quick and easy (and free) for people to leave comments about your UI. I do believe there is a charge for submitting your own UI designs for feedback though. I have only ever used it to take part in tests, not to get feedback on my own designs so I can't vouch for how useful the feedback recieved is.
Forrst.com is an emerging UI design community site that I have come to enjoy. Give it a whirl.
I recommend www.usertesting.com.
You get a video of a user talking about your webpage. You choose the questions they answer.
Downside is it's a little on the expensive side, at $29-$39 per test. However I think getting feedback from users can be more much helpful that just getting feedback from other designers.
For a starter you can post it here and users of UX stackexchange will do the honor to help you with your design feedbacks.
Another website community you can post your design is Dribbble. It is a good design community wherein you can share and have some feedbacks from awesome designers all around the world.
For specific UX questions this site here is a great resource, but it is not the best place to go for general "what do you think of my design?" questions. For quick feedback I like fivesecondtest, for longer answers you may want to try conceptfeedback (it's a little bit focused on the graphical side but you can get valuable UX advice there as well).
Forrst.com and Dribbble.com (on invitations) are the most used online resources. Because to really have feedback from a community you first need a strong community. And since those two sites are here for a while now, you'll get precious feedback. I can add Behance.net and Lovedsgn.com that are also well spread among the community.