One of the more interesting trends coming out is the proliferation of plastic, low cost lenses. This has been a trend with zooms for some time now, but the interesting development is the range of primes and more specialised lenses with this philosophy. These lenses are generally very light, but with no skimping on the optics.
The proliferation is interesting - Sony released their DT series lenses for alpha A mount cameras, Pentax introduced a 35mm f2.4, Nikon the 40mm macro and jest recently Sigma has launched the 30mm f2.8 for NEX and M4/3 cameras.
I like and applaud this trend. Sure there's nothing like a solid feeling highly capable lens, but being able to get almost the same thing for a quarter the price is extremely appealing.