Many thanks Guys for taking the time to help and advise. I appreciate it!

As someone new to Digital Photography, I have a K10D fitted with a Tamron 18-250mm zoom. I am looking for some advice about lenses to complement this good but rather 'all in one' lens. I'm going on a special holiday to Vietnam and Cambodia soon and expect to take lots of landscapes and buildings, especially the temples at Angkor Wat. Any advice please gratefully received!