Toledo is a native 1MB L2 design. (All Opterons and some X2s)
Manchester is a native 512KB L2 design. (Some X2s and A64 single core CPUs)
So a X2 3800+ Toledo is a core originally manufactured with 1MB of L2 cache, but half of it is disabled. X2 3800+ Manchester is designed ground-up with 512KB of L2 cache. The end result is the same 512KB of L2.
Which one is better is debatable. I've seen many Toledo cores clocking better than Manchester cores despite the larger L2, but Manchester seems to run cooler and eats less power. But in the end the difference is negligible, I think.