doing the same, possibly, so i'm looking forward to what the experienced have to say. i'm sure you've checked this out: http://www.cxmagazine.com/how-to-convert-your-bike-to-singlespeed (which has some info on tensioning). there's also this http://cowbell.cxmagazine.com/forum/topics/single-speed-riders-do-y...
and this is interesting...homebrewed versions (mtbikes, yeah, but universal in application...check out the Spoon): http://forums.mtbr.com/singlespeed/pics-homebrew-chain-tensioners-2...
This one is killer: http://labs.yesspro.com/products/etr-v
Compact, reliable, strong and easy to set-up. And looks good, too.
I had one in my singlespeed and it worked perfectly fine.
I have a simple one from DMR Bikes. No slip. I run single speed cassette cogs which have longer teeth, and a singlespeed chain. The other thing is it at all possible push UP with the tensioner, not down, it gives the chain more engagement with the cogs teeth. Using singlespeed chain, you can also get 1/2 links to fine tune your chain length, and a straight chainline is essential. I use two master links and have several short sections of differing lengths for different gear combos.