I have had very good luck with ceTe Dynamic PDF but it won't work for anyone who needs export in RTF, TIFF, etc. (it just outputs PDF files).
I've tried Telerik Reports and liked it although you'll want to take time to evaluate the data handling aspects as I found this aspect of the product a bit clumsy. However, Telerik's overall reputation is very good and their other products (which I do use) are top notch. Overall, my sense is that, once you are used to it, you'll find Telerik Reporting to be very good.
I also tried the DevExpress product and, as of October 2008, it seemed as if it wasn't quite ready for prime time. Their Grid products are very good but I could not in good conscience recommend their reporting product.
I am not a fan of the Microsoft Reporting Services (which I also evaluated at length). While I respect the scaleability of the product, it simply should not take that much effort to get the reporting infrastructure up and running. It is very much overkill for most web applications.
Finally, someone else recommended Active Reports. I tried it briefly but didn't find much advantage over Telerik and it is very expensive.