We also LOVE LOVE LOVE our Keurig! We've had ours for over a year and a half now (almost two years) and love having it. We recently stopped drinking coffee (I never really liked it and DH was up to over 6 cups a day - it was screwing up his sleep patterns, so he quit), but we still use it (at least once a day) for tea. The first year alone I'm convinced that we saved enough money by not going out for coffee to pay for the machine!
DH really liked the Tully's coffee K-Cups and the Newman's Own ones, but he likes his coffee pretty strong (he even brewed it on the middle setting and not the large one!

). I really like the Bigelow Breakfast Blend, Green Tea and I Love Lemon (add a little lemon juice and honey if you have a sore throat - it's great!). It's easier to find the Bigelow teas in Canada (I also drink Twinings, but it's harder to find them up here for some reason).
We also have the K-cup thing where you fill it yourself with your own coffee. While it's nice to have (especially if you're picky about the coffee you drink), they are a bit more of a hassle.
If you're big tea drinkers, remember that you can also "brew" hot water (with no K-cup in the slot) with tea bags or loose tea. While we do keep tea K-cups around, we rarely use them - we use loose tea or tea bags more often (I realize that then you have to wait for the tea to brew so it kinda defeats half of the purpose of the time saving

). We often make our own ice tea using two tea bags and then pour over ice.
We also use the hot water for soaking ramen and rice noodles too, which is nice to not have to plug in a kettle.