Sony ACID (several versions)
Sony offers several options, at different price points. Suggest you read their product pages to see which best fits what your friend wants to accomplish.
Sony ACID XMC - $40USD
http://www.sonymediasoftware.com/products/showproduct.asp?pid=987
Sony ACID Music Studio - $70USD
http://www.sonymediasoftware.com/products/showproduct.asp?pid=971
Sony ACID Pro 5 - $300USD
http://www.sonymediasoftware.com/products/showproduct.asp?pid=928
All are loop-based, like Garage Band. I believe all also offer recording options (instrument, microphone, etc.). Sony also offers a large selection of loop libraries (
http://www.sonymediasoftware.com/loop_libraries/content.asp ).
They have what appears to be a nice user site, ACIDPlanet (
http://www.acidplanet.com/ ), where your friend can download free loops, listen to the creations by other users, participate in forum discussions, etc.
I've used an earlier version, ACID 3.0, back when it was owned by Sonic Foundry. I haven't used it in several years, but when I first played around with Garage Band, I remember thinking it was very much like ACID. I recall that it was pretty easy to get started with, but I only scratched the surface of its capabilities (much like with Garage Band). I'm not a musician (the only musical instrument I can play is the stereo), so I've only played around with ACID and Garage Band, and can offer no other commentary on them. But I suspect your musician friend will find one of the ACID offerings a fun and useful gift.
Edited to fix loop library link.