Nowadays is really difficult to be up to date with the latest technologies, concepts or tools. There are several ways to accomplish this. You could use RSS, check blogs regularly or follow as many people as possible in Twitter/Facebook. My way is to watch videos from various conferences.

There are few things, which I'm looking for while picking a conference to watch.

speakers - I know a lot of good speakers and if I see them attending in an event I know that I have to check it. That's how I found the smart people. Usually the they are, or at least have something smart to say.

talks - I'm interested in tech talks, but not lectures with a lot of details. I prefer to listen for a new concept or some interesting use cases. If the slides are full with complex I feel a little bit bored and normally I move to the next speaker in the list.

only new stuff - there are a lot of screencasts out there. It is physically not possible to watch them all. I have a simple rule - watch only those clips which are captured this or last year. Of course I have exclusions, but in general I'm trying to stick to the latest videos.

Front-Trends

That's maybe my favorite. Really interesting speakers, various technologies and reasonable timeframe for the talks. It's a conference happening in Europe, Poland.

Official page: front-trends.com

Videos: https://vimeo.com/fronttrends

Fronteers

If you are front-end developer you should definitely check this out. The talks are 40 minutes and 10 minutes Q&A. The conference is placed in Amsterdam.

Official page: fronteers.nl

Videos: https://vimeo.com/fronteers

JSConf

We all see the rise of the JavaScript. Everyone is talking about it, everyone is using it. However, this conference is not only about JavaScript. It's worth checking it out.

Official page: jsconf.com

Videos: playlists in YouTube

BDConf

It's an event about the new technologies, mobile web. Really helpful talks about responsive/adaptive design, modern concepts, new workflows etc ...

Official page: bdconf.com

Videos: https://vimeo.com/bdconf

Mobilism

Mobile, mobile, mobile ... Nowadays everything is around those mobile devices. It's really great that there is a conference organized about the subject.

Official page: mobilism.com

Videos: https://vimeo.com/webconferences

FluentConf

That's a conference organized by O'Reilly. We all know their contribution to the development world.

Offical page: fluentconf.com

Videos: videos at YouTube

XOXO Fest

XOXO is an experimental festival celebrating independently-produced art and technology.

Official page: xoxofest.com

An event apart

An Event Apart is an intensely educational two-day learning session for passionate practitioners of standards-based web design.

Official page: http://aneventapart.com/

Videos: https://vimeo.com/zeldman

Webshaped

A conferences happening in Finland. Just check the speakers and I'm sure you will bookmark the videos link below.

Official page: webshaped.fi

Videos: https://vimeo.com/webshaped

Kod.io, Linz.kod.io, CodeFront, JStanbul, JSPYconf, JSIST

There are several conferences organized by the guys from WebBox. They all deserve visiting.

kod.io, linz.kod.io, codefront.io, jstanbul.org, jspyconf.org, jsist.org

CSSConf

A conference dedicated to one of the most popular languages in the today's Web - CSS.

cssconf.com, cssconf.eu

SmashingConf

We all know SmashingMagazine. Every developer lands on that site almost every day. So, that's a conference run by the same people. Great speakers and great talks.

smashingconf.com

Border:none

A novel 2-day concept conference about the decentralization of the web, featuring inspiring talks and creative sessions, spreading over several outstanding venues in medieval Nuremberg. Shaping the event lies in your hands — start participating right away.

border-none.net

Beyond Tellerrand

The affordable 3-day event with intensive workshops and high quality talks for web enthusiasts.

beyondtellerrand.com

Here are few other events that I wasn't able to find screencasts from (or at least for most of them), but they are still pretty interesting:

If you want more I strongly recommend checking links like this one. SmashingMagazine regularly post such articles.