I may be biased, but I'm really looking forward to OS 2.0. It not only includes native email, but also lets you juggle multiple emails, and multiple email accounts, simultaneously. Mind you, there's a lot more to OS 2.0 than cool new email features. To get a taste of what's in store, check out this walkthrough with Jeff Gadway of RIM:
This video doesn't touch on everything that's new in OS 2. For additional features, check out the RIM press release, which provides a good overview.