An alexandrite engagement ring - is very nice choice. Alexandrite is a beautiful gemstone and an excellent stone for the ring, but it can be expensive... and I mean a lot more expensive than any diamond ring. Diamonds may be a girl's best friend (and they defiantly should be side stones in your ring), but an alexandrite rings is something very very special.
Here is a photo of a beautiful ring featuring a fine Indian Alexandrite. Alexandrites from this deposit are well known for their exceptional daylight blue green colors. The center stone is encircled by high quality diamonds that continue along the shank from every side and through out the under gallery.
Check this store for more alexandrite rings: http://www.davidwein.com/