Solaris x86 is still quite viable, especially in Solaris 10. Oh, and Sol10 is now free as well.
My HP notebook specified below has plans to be part Solaris 10, and I did run it briefly in 64-bit mode.
I strongly suggest staying away from a SPARC notebook. We had a couple at work, some of the most interesting lead weights on the planet, though they did in fact run Solaris/SPARC (after MUCH fighting with various drivers and special machinations which we were not happy about). However, it became easier to get something like an IBM notebook to run against a little 1U style SPARC (like the V210 today). Hell of a lot cheaper too.
If you're still needing a true SPARC notebook, Sun now sells their own apparently (maybe a rebrand), under the Ultra 3 line:http://store.sun.com/CMTemplate/CESe...P&catid=132680
Warning, they range from $3.5K to $10K on that page.
Cheaper to get a second-hand SPARC desktop like the workhorse Ultra-2 (which I recommend highly, though its SBUS) from somewhere like eBay. If you want PCI, than look into second-hand Ultra 10. Ultra 5 should be ignored highly unless you're stripping for parts (most of the internals can be used on the 10).
Hope this helps,