The D521 rim is reasonably strong.  It is also quite light as well. This makes it suitable for trials.  It is also at an excellent price of around £19.99, which makes this rim really worth getting.  There is also a CD and Ceramic version available too.  

The CD (top)  is anodized for even more strength and priced at £28.99.  I believe that it is better buying the CD version for that extra £8.99, as they do appear more durable to me and dirt isn't as clearly visible.

The Ceramic version  is also anodized for strength (CD).  It also contains a special coating on the braking surface to improve the braking performance.  This rims costs about £45.  Which in my opinion isn't worth it.  As I have heard on a numerous of occasions that the braking surface completely wears down after a fairly short period of time.