A significant advantage of working in software development is that we have lots of excellent conferences we can attend. This is an unusual phenomenon compared with mainstream professions. Folks who work in paper-pushing industries typically have their choice of only a handful events a year, with one show being a must-attend and the others being entirely optional. Those events are also rather unlike programming conclaves. They're typically junkets in which attendees participate only to hear keynotes or product introductions, and meet a few contacts. They then spend the rest of the time MIA.
While developer conferences can have some of the same aspects, they generally do not. Programmers are far too engaged in their projects to waste the opportunities for soaking up more knowledge, meeting colleagues, getting free T-shirts, and eating pizza. The key, though, is undoubtedly the pursuit of knowledge; and here, most of us can choose from a wide range of options from large multi-day events to small intimate meetings.
Below, in chronological order, is a commented list of conferences that I believe are worth attending. I've either been to them in the past or have spoken with enough folks who have to glean a pretty good sense of them. I indicate which is which.
OSCON (Portland, Oregon, July 25-29) is the big jamboree for open-source developers. Consistent with the bazaar image of OSS, the conference touches on new open-source products, new languages, and tutorials on how to program with OSS tools. To put a little order in things, O'Reilly has created two new tracks: Big Data and Java (so much for Java's imminent demise!). I've attended this conference four of the last five years and have loved it. I'll go again this year if time allows.
Intel Developer Forum (San Francisco, September 13-15) is one of the few vendor conferences that is truly worth attending (Google I/O, JavaOne, and Microsoft PDC, being the others). If you're into processors at all, this is nerd-stim taken to a very high level. Exploring multicore architectures, virtualization, cache hierarchies, and so on can be pursued to lengths that cannot be reached elsewhere. I've probably been to this conference more than any other.
StrangeLoop (St. Louis, September 18-20) is a comparatively new conference that focuses on emerging languages, big data, distributed systems, and web programming. Sessions tend to be technically very deep. I have not attended it yet, but have heard consistently good things.
JavaOne (San Francisco, October 2-6) is the center of all things Java. While there are several other good Java conferences, this is the one where you'll find the most classes on virtually every Java technology as well as the most vendors. The wide selection of classes and workshops makes it possible to get in-depth exposure to technologies that interest you. Last year was the first time that JavaOne was held under the Oracle aegis, and frankly, it was disappointing. Google had just pulled out leaving plenty of holes in the schedule and Oracle had not planned the conference well. This year's event is probably make-or-break, so I'm expecting a good show and plenty of knowledge transfer on Java 7.
QCon (San Francisco, November 14-18) is a tutorial-intensive conference aimed at architects and project managers (so, not quite the dirt-under-your-fingernails feel). It attracts big-name speakers and is well respected. I've never been, but I've heard good things. I expect to attend this year.
Citcon (October, European site to be announced on Citconf.com) is a three-times-a-year conference (in the spring, it's held in North America, summer in Asia/Pacific, and fall in Europe). It's free to attend and is built around the open spaces concept. This approach asks attendees over the space of a couple of hours which classes they'd like to attend. The most popular ones are then scheduled. You're then free to drift in and out of the sessions to find the one you most like. Attendance is small, but classes are intimate. Meals and drinks are provided. Themes are mostly about testing, continuous integration, and management of development processes. I've been to two Citcons.
Devoxx (Antwerp, November) is a smaller version of JavaOne, without the Oracle agenda and with somewhat more focus on presenting open-source projects. It's very popular in Europe and is the largest Java conference outside of JavaOne. I've never attended to my detriment.
I find that with the exception of bring-your-laptop workshops and labs, it's difficult to acquire deep learning of a topic at conferences, especially at the large ones. Rarely, do you find a session that's targeted at exactly your skill level (with the notable exception being presentations of entirely new technologies). However, conferences are excellent places to pick up insights and new perspectives: doing something unexpected with a tool you know, grokking why some technology has a specific design, discovering that everyone uses a product differently from you, and so on. And for those insights, there is no substitute for in-person attendance.