I am going to be setting up an all-grain setup here in the next couple weeks, probably with a cooler mash-tun and outdoor propane cooker. I am planning on just doing 5 gallons to start, and am just trying to figure out how powerful of a burner I need (in BTU's). Obviously it would be great to get a burner with a quarter million BTU's, but is that necessary, and can I get relatively good boil times with 50000-100000 BTU's. Thanks.

Dave

These are the burners I use on my converted kegs and they work great.

http://bayouclassicdepot.com/bg10_cast_iron_burner.htm

I use a couple of the style Badrock listed, but they are really loud when going "full bore", you might want to concider this other style from the same website:

http://bayouclassicdepot.com/bg12_cast_iron_burner.htm

This is much quieter than the "Hurricane" style. The good thing about either style is that they are cheap, so if you aren't totally happy with the ones you purchase, you can try others.
Good luck,
-Greg

This is the one I use. Plenty of BTUs on this one!
http://pixdaus.com/pics/1242414567VnUntxe.jpg

I use the same as Otterbrew on my system and they work great for me. By the time the HLT and mash has reached temp, I have weighed and milled the grains with little time wasted waiting for heating. As I'm sparging, I am heating the collected wort, so by the time I am done there isn't much time before the boil temps are reached. On the boil, I run the burner at 1/2 to 1/4 output, so I don't believe a higher output burner would be necessary. In addition, these burners spread out the heat a bit more than the jet burner and are much quieter.

just my 2 cents.