For the small grower:
http://sensiblesurvival.blogspot.co.uk/2014/03/build-hand-held-corn-and-bean-planter.html
There are absolutely tools that are some to much faster, but they're also more than $5-15 bucks. Mother Earth News did a nice review of some walk-behinds not too long ago:
http://www.motherearthnews.com/homesteading-and-livestock/garden-seed-planter-zm0z12jjzsch.aspx#axzz325CU3KKS
Here's another with stab planters (kind of what the first guy built):
http://www.fs.fed.us/t-d/pubs/htmlpubs/htm10242306/

I made a mini hole press out of a bike tire, just drilling holes and adding screws for 1/4", 1/2" and 3/4" depth for the ability to wheel over and make holes from 2" to 18" apart, but it didn't have a delivery system for seeds that ever worked (wasn't reliable in how many seeds would pass, sometimes blanks, sometimes 2-3 escapees, sometimes escapees between holes).

I like the simple "doh" tube especially for people whose 1-3 hours of bending for planting ends up leaving twinges in the back for a week, especially for a small space.

I've been playing a little bit and when I make this for my parents, I'm actually going to use a joint at the dirt end that will let them do holes at 3", 4", 6", 9" and 12" since those are the most common, and just mark it in yellow, red, and blue for the three common depths.
I'm still working out if it'll be easier to make a screw-on joint for each size or if I want to work out a little clamp that can just be slid along a bar.

Admittedly, it's not perfect.
In testing, the hole-poker length is important.
You have to be able to press the hole deep enough without that pressure also caving in the hole you just poked, but too high up, you end up missing the hole. I cut a little funnel so the poked seed holes are about 1/2-3/4" wide and the seed funnel is just wide enough for a kidney bean. Funnel will have to come off with a hose clamp for limas or favas.
Tiny seeds might not seem worth it, but the 2' test is actually smooth enough especially with the funnel to do onion, chives, borage, and some of the little round mustards and lettuces. Teeny-tiny poppy/clover/lemon balm-sized stuff is so hard to tell, no matter what you do, but on the carpet they were rolling through just fine in pairs and trios. They'll catch on rough edges, though, so thumping the tube helps prevent just 1-2 seeds of 4 here and then 9 falling off there.

Moms is gonna be thrilled when I add this ugliness to her shed, Pops starts his own tinkering, and it breeds like a wet Mogwai. 🙂

I wish a tube had occurred to me when I was maintaining 1/2-1 acre of garden at various times. Even just using a marked dowel for depth and the holes and a separate piece of pipe to drop seeds down would have saved a lot of backaches during planting.

Hopefully, somebody else can use the oober-simple chimp tools, the nifty two-prong DIY, or even one of the commercial units.
For more than an acre of row-crop annuals, I would totally spend $100 on a walk behind at this point in my life.