I'm a little late to the party, but on 4/29/2011 Ruger finally released a factory 25 round magazine for 10/22 rifles and variants:

http://www.ruger.com/news/2011-04-29b.html

Model BX-25

Stainless steel lips and spring. Ruger name on the side. Thirty bucks.

I decided to bite and purchase a couple of them:

Order placed Friday 4/29-backordered.
Order shipped Wednesday 5/4
USPS attempted insured delivery on Friday 5/6, but I wasn't home
Finally was able to make it to the post office yesterday to pick them up.

Pics:
Packaging, comes with disasembly/assembly instructions. Needs a 3/32 hex head (not included) to disassemble.


out of the package, side view:


comparison of three magazines (all new):
Butler Creek steel lips 25 round mag, Ruger BX-25 and Eagle 30 round mag


Feed lips:
Left is Butler Creek steel lips, center is Ruger BX-25 and right is Eagle 30 round mag


No range report yet, but the Ruger looks and feels good, but then again I've had no problems with either the Butler Creek or the Eagle magazines that I've used over the years.