Price: $2.99
Pros: Makes racking incredibly easy and eliminates the need for an auto-siphon.
Cons: Nada
Recommended? Yes

Comments: These are so far superior to drilled rubber stoppers that comparing the two is like comparing a log and a wagon; they both get the job done but one is vastly superior to the other. When it comes time to rack simply replace your airlock with a racking cane and pressurize the other nipple on the cap with CO2 or by blowing into it (what I do) and the beer in the carboy will be pushed up and out of the racking cane. No auto-siphon to sterilize or even own.

YouTube - Home Brewing Tools : Home-Brewing Carboy Cap

Price: $10.00
Recommended? Yes

Comments: Just your regular wing capper and bottle caps. Don't know what this carboy caps are...?

Pros: Easy to use and versitle.
Cons: Losing the little white caps -grrrrrr.
Recommended? Yes

Comments: Whoever thought these things up is my hero. Far superior to rubber stoppers in many ways. I use them for racking, blowoff and airlocks.
I have had rubber stoppers after sanitizing and installing one with a airlock, pop out of the carboy within as soon as I turned my back. Before I got the Universal Caps I used to spritz acholol around my rubber bung and the opening of the carboy, dry both with a paper towel so it would be "gummy" enough to stay in. Universal Caps just snap right on, no worrys.
As for racking, my favorite way is to put the racking cane in the middle, sanitize it and use CO2 in the offset nipple to push CO2 into the carboy to start the siphon. Keeps a CO2 blanket on my beer and because I put CO2 into the receiving bottling bucket or secondary carboy, I keep a blanket of CO2 there also.
These things are so useful, I thought I might drill holes in my TV trays and stick the nipples in the holes to make a glass holder - just kidding! Mmmmmm?

Pros: One size fits all
Cons: None
Recommended? Yes

Comments: I wouldn't ever use anything else. I have two of these. They are perfect for an airlock & blow off.

Pros: Ease of use, sturdy construction
Cons: those are the only colors.
Recommended? Yes

Comments: While I've never used them for racking at all, they are an excellent replacement for the drilled rubber stopper. Since this doesn't get pushed down into the neck, it would take a concerted effort to force one of these into a carboy. Additionally, it is almost impossible not to put this on correctly as there is a distinct feel when the cap is pressed home.

Price: $1.99
Pros: Start the syphon with a simple suck or blow on the other tube.
Cons: requires 2 racking canes when moving from bucket to carboy
Recommended? Yes

Comments: These come in 2 sizes. One for the normal 5-6 gallon carboys and one for the larger 6+ gallon.. I bought one for both and I would say it's made racking a whole lot easier.. No longer have any issues moving beer from one fermenter to another... Sanitizing is a breeze too! Also can be used as a plug to hold your airlock if you are in a pinch.