Matt,
Congratulations on your new purchase.
I will also vouch for the Canon EF 24-105 f/4
L IS USM lens. It is tops.
If you'd like to see some images, head on over to the terrestrial photography section and have a look at a few of my latest shots.
If you do end up purchasing an L you're going to be spoilt. I ghettoed it up using standard EF lenses for a long time, and even did a fair amount of astrophotography using them (do a search in the deep sky forum for my posts). The moment I put the new lens on... wow! You notice the vibrance and sharpness, immediately.
If you're not in a position to splurge and are after a standard all round performer, I strongly recommend the Canon EF 50mm f/1.4 over the f/1.8. For starters it is built a lot better and is faster. I've been able to shoot New Years Eve fireworks with that lens in fully automatic mode, whilst on a boat on the harbour, and the images have come out superb.
Also, listen to Andrew. 
Regards,
Humayun