There’s never been a better time to be an Internet startup, and not only because companies such as Google, eBay and Microsoft may buy you out for a few hundred million dollars. The initial public offering (IPO) market is also especially aggressive these days, and LinkedIn — the social network for business professionals — was the most recent high-profile startup to reap the rewards. As expected, the company’s public offering in May was an enormous success, following the recent trend of staggering IPOs from Web startups such as Renren, Demand Media and ZipCar. The big three, of course, that everyone is excitedly eyeing now are Zynga, Groupon and Facebook, which is now valued at more than $50 billion.