Hmm...well given my inability to show self control around my homebrews, this has never been an issue. I would be curious how pasteurizing would effect the taste over time. At any rate, a beer should be good on the shelf for at least a year, probably past that. If what you brewed was a great beer, BREW IT AGAIN! Replication is important when creating something truly great, so why not drink what you've let sit for a couple months, brew more of the same, and repeat as many times as possible!
I can understand the allure of wanting to keep a solid beer on the shelf for 2 or 3 years, but I can't help but feel that brewing more beer is the answer. If that isn't the answer, you're not asking the right questions.