Folks, we've got a crisis on our hands; one that you've probably heard about already but bears repeating. It's called Colony Collapse Disorder, and it means that honey bees--our top insect pollinators, partly responsible for ensuring that crops successfully produce and bear fruit--are strangely disappearing. They need all the help they can get right now, and there are a few simple things you can do (provided you're not allergic, of course) to help the bees get back on their feet--err, wings.
Part of the problem bees are facing, according to books like Fruitless Fall by Rowan Jacobsen, is the lack of flowering plant variety.
Since bees do best in environments that offer great plant diversity, so in addition to the seeds you're starting for your spring fruit and veggie gardens, sow some from this bee-friendly list. Flowers native to your area are best, of course, so ask your local plant gurus (think nurseries, farmer's markets, etc.) what would do the trick.
If your city allows it (check the ordinances), and your neighbors are cool with it, and you're up for the bit of work entailed (yes, that's a long list of pre-recs, but...) look into backyard beekeeping. There is a wealth of information online, of course, but visit the library to find beekeeping books and be sure to read up before starting a hive. We're in the very beginning stages of putting hives out on two family farms, which means we're investigating everything from costs to upkeep to what to do in the event of bee mutiny.
If you want to invite the bees but don't want to keep a hive, look into other bee homes like these, or this one.
And without touching the bees at all, you can help out by supporting your local farmers and purchasing local honey. Not only will it taste like your surroundings (fields of wildflowers or clovers, for instance), but it's great for alleviating local allergies.
Photo by gklinek via sxc.hu.

Sheex Bedding
Bees love our rosemary, which is why we'll continue to grow more than we need.
I read something totally anecdotal recently, suggesting that perhaps early-morning watering cycles are washing away nectar. The writer (sorry, can't remember who, or where I read it) started watering in late evening instead and noticed that the bees came back. His theory is that watering when flowers are open leads to bee starvation. Thoughts?
Mother Nature (rain) does not water only in the evening or only in the morning time... She has her own schedule.
Some say evening watering can cause root rot. I have not experienced that, but I only water in the evening once in a while when I've run short on morning time and have to zip out quickly.
Perhaps water from the base of the plant, not the top.
There is no clinical data that corroborates the suggestion that eating local honey will lessen one's allergic reactions to local flora. If you have some I would appreciate a link.
It's anecdotal, SunnyBlue, but I've noticed that my allergies flared up when we moved here (to CA from TX) and I've added local honey to almost everything I've cooked (And we cook 3 meals a day) and my allergies have calmed in a matter of months.
Does the honey get all of the credit? I don't know, and frankly, it's working and it's tasty, so I don't care.
Bonus - we have lots of flowering fruit trees around our house and I've noticed they buzz with activity (literally) almost all day every day.
When I plant more, (If I plant more) I will certainly use your bee-friendly list.
htpp://embritadesign.blogspot.com
Amberb: Thanks for bringing this issue to the readers. Good suggestions, esp. notes on variety & native plant use.
For your family farms, I hope you consider incorporating methods of inviting native bees. Encouraging native habitat in the farm area is one of them.
Relevant research has been done by Clare Kremen at Univ. of California, Berkeley, and also Sarah Greenleaf at UC Davis -- for example.
A discussion of this topic is here: http://www.ethicurean.com/2009/02/09/buzzkill-can-native-bees-do-the-job/
(and many other places).
Another reference:
"Farming for Bees: Guidelines for Providing Native Bee
Habitat on Farms" published by Xerces Society for Invertebrate Conservation.
www.xerces.org
Good luck.