Kettlebells are great...I'm pretty new to them and still trying not to cosh myself with them, however they're another fun way to cross-train...
TRX is wonderful too-expensive, but I use it a lot.
I"m waiting a little while on the BOSU-got the DVD set on sale, but my husband is going to have an aneurism if I spend any more on fitness items for a month or two (he doesn't have to know if I get just a few more Cathe dvds though).