As expected it's very hard to get an employer to pay attention to you when you're far away unless you've done something truly special or they've had a chance to work with you personally/face to face over a period of time. Unfortunately the bad economy isn't helping, there are still plenty of americans without jobs so getting a work visa is hard.

Networking, volunteering, internships all can help get at least a referral, maybe it's possible to do some of these or try and start at your next work/travel program. Focus on a geographical area where you meet lots of people in the industry you're interested in, for example life sciences has a big focus in San Diego, internet startups in Silicon Valley, finance in NYC etc. For a company to sponsor your visa there's quite a few financial and paperwork hoops for them to jump through so you really need to stand out.

Good luck.