Cog Guard?
 

Do they make guards to keep your pant legs out of the cogs? I keep ripping my pants.

MTB or road?

roll your pant leg up. problem solved.

you can also use a rbber band or a velcro strap that is for that purpose or, if you can find them, go old school and use the metal pants clips.
If you are not a slave to fashion, straight leg jeans don't get caught in the chain. They do get kind of dirty, tho.

Yes:
You can get plastic or Al rings to go outside the chainrings.
Full-length chainguards to protect you from the top of the chain, (these can work with triple chainring systems as found on European city bikes.)
Fully enclosed chaincases, these work with singlespeed and hub gear systems.

Finding a chainguard in the US may be a problem. They can be had from some UK mail order houses, but you are better off with a continental euro place.
I use trouser clips to keep my trousers (US pants) clean.

i use the velcro reflective straps. they have the added advantage of night visibility.

just fold the jean pant-leg over and wrap the velcro strap and done -- i wear really baggy jeans so i MUST use them but i find the pantsleg in the socks dorky and rolling always seems to some undone at a bad time.

you can buy them at most bike shops for a buck or 2

If you go with a velcro strap, make sure it has neoprene incorporated as well. Velcro-only can cut into your ankle with each movement. :o Metal clips can also dig into your ankle but that may differ per person.

Sp@eder

Another vote for the Velcroe straps. I've used them many times for the occasional shorter trips on the road when I don't need to get into the whole padded shorts/jersey outfit.

-Moab

i also use velcro... seems to work alright.... but i hate it when i forget to take it off... hahahah