The best way to be inspired is to do something inspiring, I realized a while back. But, it's hard coming up with answers when you're uninspired. I've tried many things, but found nothing that inspires me to continue a task (yes, it seems like that at this point) I've been performing all day.
Where? How? What? And it makes you want to write MORE code??
I find listening to music while I code (not excessively loud) keeps me less bored. The longer you are thinking of how bored you are the faster you will want to quit.
When working for an employer however, a paycheck is a big inspiration.
Take a quick nap
Or, one thing I like to do is quit coding and write an outline of what I want/need to code. With sufficient prior planning I tend to get excited about some interesting code segment and jump back in. You're right to keep it in your head though.
Although at times it's ok to step back and take a break.
I find it interesting to learn about other programming languages, even though I don't end up using most of them. If you work with a single language from day to day, reading some tutorials on other languages or studying topics like project management can be a breath of fresh air (something new, still relevant to your job). It can give you a fresh perspective also.
Perusing Slashdot will expose you to problems and solutions of using a -wide- variety of technologies, and Digg has a Programming section, showcasing top-rated programming web pages. It is interesting to hear about other programmer's experiences by following their blogs.
Oddly enough, some new studies are coming out to say that it isn't a given chemical that can perk somebody up, but the anticipation of the "energy boost" that does some wonders and all you need to do is give your brain a boost.
Late at night, or sometimes in the morning when I'm trying to wake up to take care of the kids, I'll often think about how I'm going to implement a given feature or solve a particular problem people are reporting, or even was awesome new thing I'm going to add to my pet project and that seems to get me plenty awake and motivated before the coffee settles in. You might try this "brain boost" yourself.
That or maybe I'm just messed up in the head...
Grab a cup of coffee and take a walk. Try to talk with someone about anything but code (with another cup of coffe if you need.. :p). The point is to let your brain relax. If you come back about 10 or 15 minutes later, you'll feel much better.
Drop by StackOverflow
and then you go back to your own coding and you're good for another while...
1) If you're talking about working on a side project after spending all day writing code at your day job, try focusing on the things that got you excited about your side project in the first place.
2) Do the fun stuff first. It's easier to keep coding than to start coding, and it's easier to start coding the fun stuff.
3) Write the simplest end-to-end system you can that will work, and then flesh in all the real functionality later. Nothing gets me excited about a project like seeing it Actually Work Right There In Front Of Me.
4) If you're talking about working on the same project all day long, and then working on it some more after hours in front of the screen... take a break! Go run around the block or eat a sandwich or something. Let your brain wander and make connections on its own - if you end up thinking about the project, awesome, but if you don't, that's fine too.
5) Try changing your setting. Go to the local coffee shop or something. Read about Nomadic Programming.
6) Talk about it with a friend. Again, try to focus on the cool stuff and the tricky problems, and let the conversation wander if that's where it goes.
7) Some days it just isn't going to happen. Come back tomorrow. Try not to worry about it too much - sometimes that's just how it goes.
One thing inspires me to write code more is competition. Not that I want to be better than everyone or show everyone my 1337 skillz - it's more humbling really - but that the competition challenges me to push myself and I end up being able to see myself improve.
my outlets:
topcoder
codegolf
usaco
etc.
something that is cool to do when you're too pooped to code is just pick up the notepad and brainstorm. That tends to inspire me and i like to draw meaningless diagrams and relational charts.
i find gaming is a bad idea because I end up just gaming all the time and not coding... ever. :P I know i never thot i'd say it.
I usually Take a break... Do something physical, mow the lawn, go for a walk, etc. For at least 30 minutes.
Then I usually come back feeling refreshed. Especially if I have been working on a particular problem for more than a couple hours and are getting no where... A lot of times fresh ideas pop in my head when I am not thinking about it, if that makes any sense...
I normally take a shower. It makes me concentrate and relax. Music is also a factor. Depending on the need I follow two styles: soundtracks for design and progressive metal for coding.
And I walk. Sometimes I have a problem while coding, and I start walking around and thinking.
Everyone has his methods. You have to find your own.