"I don't blame my boyfriend, he only beats me when I deserve it."
You learn many valuable lessons on that first job. One of them is that if they pay you cheaply initially they will almost never see you as "valuable" after that. It's just human nature. Another lesson is that the best way to get a raise is to switch jobs.
HN's patio11 has perhaps the most awesome blog post on salary negotiations. http://www.kalzumeus.com/2012/01/23/salary-negotiation/
Good luck and stay strong bro.
I remember at my second job, I discovered that a co-worker who worked there longer, made less money than I did, and I considered myself underpaid. And that was actually a pretty nice company with decent founders. The co-worker started there as a student I think, and maybe he was never assertive enough in asking for raises, or maybe a bunch of 5% raises still don't amount to much if you start low enough.
Whatever the case, I learned through personal experience that the best way to get a raise is to switch jobs. For some reason, it seems you have more leverage with a prospective employer than with a current one.
The good news is that when I left I they gave him a huge raise, I think they doubled his salary.
edit: I wrestled with bringing this up, but you mention several times what kind of laptop you had versus what kind your coworkers had and that you bought an unaffordable laptop for a part time internship. You can usually find passable used laptops on craigslist and such that are very inexpensive. Getting by on one of those is a lot more impressive than a loaded out Macbook, so why should this have mattered to you?
Of course, being an experienced developer, I know that the way to remedy that is not with complaints about fairness -- decision makers might not even have realized that was what I was using. Rather, pointing out the productivity benefits of having hardware similar to other devs usually seems to suffice. (Spec out a machine, propose it, etc.) It's not your machine, it's the company's, and it lets you be a more productive resource.
We all got what we were looking for. It's just a question of when you don't need that basic training anymore. Sounds like that time came for you around the same time it did for me. I can tell you - at that point, the only way up is out. You are much, much more employable now. Don't "beg for work" ... present yourself well and ask for market-rate. You said that's $75,000 in your area? Better yet, say you're looking for a range of $80-90k and see what they say.
I've got a question for you, and maybe an idea. Did you sign a non-compete agreement beyond just your term of employment?
Even if you did, it might not be enforceable in your state. Go to the billion-dollar rival and tell them how you've got almost a year of domain expertise under your belt working on a similar product. You're looking for that next step - full-time Software Engineer, and a chance to build on what you already know. You're able to make clear comparisons between the two offerings, and I bet you have some ideas about how theirs could be the best of both worlds. Oh, and when they ask you...
"Why did you leave your previous job?"
Don't panic. 18 story points on your last week, remember? You're a sharp web developer who rapidly rose in value - far faster than your perceived value to a CEO who forever saw you as "the cheap intern." Since you couldn't reach an agreement that met your salary requirements, you parted ways. Now you're able to devote more of your time to the search. That's all you need to say - so practice saying it with confidence.
Email real people at the target company (email is the new cover letter) or start asking questions on Twitter - don't just drop your resume in an upload. Start a conversation. Get your Team Lead and as many coworkers as possible to jump in with recommendations, when they ask for references.
My next offer after the internship was a real one, at market salary in Silicon Valley. There's light at the end of the first-job tunnel. It's tough now, but please believe me when I say it does get better.
I really can't post my personal account names publicly, that would give away the company and, as I've said previously, I do really like the dev team. My team leader has a kid as well and works his ass off, and I want to see that pay off for him when they get through some of the deals they're working on. There are other devs there who are really good people, including one whom I consider a friend. They all depend on it as well. Who am I to fuck with their livelihood to screw with a guy who's going to be rich regardless?
Hell, I'm not mad at the CEO either. I don't really understand if he's just forgetful, but he claims in the emails that he never said any of that about my salary. He's been running around to meetings, so I get why I'd be the last thing on his mind.
To those wondering about the financials, I know that one of their rivals (with what I consider an inferior product) is in the billion dollar club, and they're set to be profitable very soon.