I know you already said that your PC lacks an ISA slot, but that's a shame because the AWE64 is probably the best sound card for Win98SE. They're cheap. No driver hell. Win98SE has drivers built-in. Just plug it in and go. Also, excellent MS-DOS Mode support. Phil has excellent instructions on how to set this up. The only downside to the AWE64 is that it lacks EAX support, if you care about such things.
Phil loves Vortex 2 cards. He also has a list of very good reasons for preferring them over SBLive cards. I would love to try one out, but I just don't want to spend the money for one. IMO, you're gonna experience some amount of driver hell with any PCI sound card in Win98SE. Vortex 2 cards have their own issues to consider just like SBLive cards.
I'm no PCI audio card expert, but I have had very good luck with the SBLive CT4620 in Win98SE. It works extremely well with LiveWare 3 and has very good SB16 emulation. I know, you said "no Creative Labs products", but you should really consider the CT4620 if you don't want to spend cash on a Vortex 2.