Mmmmmm L series glass
Save up the money they are VERY worth it and really do change your photos.
Its the main reason that pro's photos always look that little bit better, the edge that you can't quite put your finger on, but you can see the difference and the photo just looks 'proffesional'. The secret is in the lens.
5D is a great quality prosumer camera, the sole reason why they are not used by the proffesionals is that they are not built to take as much abuse (climate sealing and construction is not up to regular workhorse abuse), other wise picture quality etc is up there with the 1 series. So it really is worth giving it the best lenses as you will get the benefit.