MightyText is available to anyone with an Android phone/tablet and a computer. It took me about a minute or two to follow the easy to understand instructions before I was sending texts from my PC.
It's a lot more seamless than other SMS from PC services with no silly plugins, downloads or software installations, which I definitely like. It works pretty much perfectly, texts appear the instant my phone receives them and there's no delay in sending texts either. Picture messages are even supported. All in all a brilliant app at the brilliant price of free.
"[There's] no silly plugins, downloads or software installations"