Christchurch itself is a lovely part of the country.  There is plenty to do, but for those wishing to take a side trip here are some suggestions.  

An ideal day trip from Christchurch is up to Kaikoura which is just over 2 and a half hours away,  for a whale watch.  (183km's)

For an overnight stay in Hanmer Springs which is about two hours north of Christchurch. (135km's)  While there visit the hot water springs and stop at Waipara wineries on the way home.  

Another side trip is to take the Trans Alpine train over to Greymouth on the West Coast and return in a day.  It's rated as one of the top 10 train rides of the world.

just over one hour from Christchurch is Akaroa. (84km's) Akaroa is the oldest town in the south island and is a lovely "French" village with cafes, etc. and makes for a beautiful drive.  There are also dolphin and penguin watch trips here.  And make a stop at Barry 's Bay Cheese factory, one of the oldest in the country. There are a few wineries one the way too.