As I have posted before, I have just purchased my first AR-15 rifle and I figured I should start doing some mag shopping before she arrives. What brand mags, preferrably 30 and 40 rounders do you guys prefer? Which ones are junk? Your opinions are greatly appreciated.

buy only mags that are USGI.

avoid USA Mags. they make good paper weights.

see the Equipment Exchange forums.

colt

never seen a 40 round mag that worked / fit well

also, welcome to the family brother!

Any U.S.G.I is good. None are any better than any other including Colt marked mags. They all had to pass U.S.G.I. acceptance standards.

I think AR's are fun if you have a mix.

20 RND USGI- Easier at the range for prone shooting than 30 rounders, plus cool looking.

30 RND USGI- Gotta have some, the standard in AR mags.  Get ones with Green followers, or buy green followers for them after (a couple bucks each) they help keep the last few rounds from jamming.  NOTE that you DON'T need green followers in 20 Rnd mags.

30 RND Thermolds- They work great, are cool looking, durable plastic, and can be had cheaper (about $20 a piece new)  
www.classicarms.org has US made new Thermolds for $20 a piece.  The Thermold mags made in Canada (maple leaf on them) have a low melting point, so stick to the non-melty American ones.

You might check out www.ammoman.com. He takes care of all of my AR mag needs. My preference is to stick with GI mags, whether 20's or 30's. Most 40's really suck regardless of who makes them.

Try this web site out.  You'll learn everything you need to know about Mil Spec magazines.

www.biggerhammer.net/ar15/magazines/makerinfo.html

Also, this one explains which mags are good and which ones are crap.

www.biggerhammer.net/ar15/magazines/rawlesfaq.html

Good luck.

USGI

You can get them on the EE, actually it's the best place on the web to get mags.  It's where I get mine.  You can expect to pay $12 to $25 for USGI's.  Watch out for some of the "range mags".