Another option for trying out a Next-Gen Amiga besides OS4 and MorphOS is AROS. There are 3 great distributions of it, Icaros Desktop, Broadway and AspireOS. Downloads of the distribution are free, and it can be installed on most generic PC's.They can't run old Amiga software directly, but can through emulation via Janus UAE.
I know CommodoreUSA has got a bit of bad press here, but you could also check out the new CommodoreOS. It is a free download from their site. I downloaded and installed it on a spare machine recently, and it actually looks very nice. It is Linux-based, but has a nice Next-Gen Amiga feel. Also, it can run the large library of Linux software.
However, like a lot of the folks here, I still have a soft spot in my heart for the classic machines which I've still managed to hold onto over the years, including my first, the A1000.