There unfortunately aren't many choices yet. The stock browser works, but it's very minimal, and slow. Evince is half-ported, and available from -devel (standard caveats apply), but while it has much better performance than the stock reader, and some other nice features, it still kills kittens from time to time, so I wouldn't recommend you use it unless you have to (I use it for reading digital textbooks so I can leave the heavy dead-tree ones in my room, and for that sort of thing, the performance is needed). If you do use Evince, note that Ctrl+Enter toggles Fullscreen - being only half-ported, it doesn't yet have the nice hidden thumb-button to get you out of fullscreen mode.
If there are any others available, I haven't tried them. Depending on what your content is like, you could always run them through a PDF->HTML converter (such as the command-line pdf2html app on Linux (I have no idea what else is out there, but probably lots)) for the mean time.
I seem to recall there being at least one other PDF reader available for Maemo 4/N8x0, so you could always try to convince someone to port it for you, or finish up the Evince port. Offering tangible forms of "encouragement" (read: bounty) is always an option, if it's worth it to you.
Sorry that I couldn't be of more help.