Allan's suggestion is a fantastic one, as you'll get to see some of the best bits of the canals. Fradley Junction is a particular favourite of mine, and you'd also go through Tixall Wide, get the industrial scenery of Wolverhampton and Birmingham, and the pretty Lapworth locks.
Alternatively, you could do the Leicester Circuit. Go up through Braunston, onto the Leicester Arm (which gives you Watford and Foxton staircase locks), onto the Trent and Mersey to Fradley, where you can either return via the Coventry Canal, or do what we did and continue to Great Haywood (which gives you Tixall Wide, Wolverhampton, Birmingham and Lapworth on the return). This would be a bit more energetic than Allan's suggestion.
On the other hand, if you wanted a quieter fortnight, you could head down the southern Oxford, spent some time in Oxford itself, go out onto the Thames, back in at Duke's Cut, and back the way you've come.
Actually, there probably are twenty ways you could go. It all depends how much time you want to spend travelling each day, and how much moored up eating/drinking/sightseeing. Where ever you end up going, I'm sure you'll have a great time.