One device called a computer will do this.  Its what I have.  I don't know if there is a simpler one.  But you can buy refurbished computer for pretty these days.

You need a TV with a VGA or DVI input or an computer with a SVideo or HDMI output.

Most Blu Ray players and video game consoles will not, however, do ESPN3 streams, if that is what you're looking for.

The space is a bit of a mess right now, based on what apps are available where. WatchESPN is currently only on Xbox 360 or AppleTV for set top devices. I'd advise against the Xbox, as it requires you to subscribe to their "Live" multiplayer service to use it as a streaming box (unless you already have one, or would want to use it for gaming).

If you have any other Apple devices, AppleTV can be a good option, as you can use an iPhone or iPad to control the box, and to load up and Airplay most media to it.

The biggest downside is compatibility, for any of these, it is often a matter of figuring out what you want to be able to watch, then deciding on a box. The only "universal" solution remains, sadly, a full fledged PC (although you can probably get away with a pretty cheap one for this purpose).

What services are you looking to watch? I'm assuming WatchESPN, but are there others that would be important to you (Netflix, Hulu, broadcast network apps, iTunes content, etc.)?

I've used laptops before for this, including those with HDMI connections.  However, my new Apple TV ($99 at Staples) is far and away better.  It has a built in WatchESPN app that works like a charm. For this to work, you must have your internet from one of the contracted providers.  In my case that's TWC.  Upon first use, you must put in your TWC username and password.  It's similar to what you have to do with your computer or tablet device.

I second the Apple TV. I love mine so much that I bought a second one for the bedroom. It costs a bit more than the other devices mentioned, but it frees up your computer, which is great, especially if you like to stream multiple games at once like I do.

If you have a Mac it also allows you to wirelessly mirror your computer's display, which is great for streaming events that aren't part of the apps Apple TV supports (like our basketball games).

I've heard mixed reviews about Google Chromecast streams from web browsers, which  you would have to do for WatchESPN/ESPN3 events). I think people were seeing really choppy video. I haven't tested it myself, but if I were you I'd go with the Apple TV.

They are $95 on Amazon with free shipping and no tax if you live in Ohio.