Where can I find sites to follow Tropical Storm activity?

There are many (mainly US based) sites which can be used to follow the progress of current tropical storm disturbances (Hurricanes, Typhoons, Tropical Depressions etc).
These two will start you off, and there are links from the Met Office url to other primary centres.

The UK Met Office Global Model is regarded highly in tropical forecasting circles, and it is appropriate that they should maintain this useful page (and associated links), from which you can 'drop-down' to other world-wide centres. Use the links in the blue panel for current activity:-

and a site that is neatly ordered, and used graphical representation of current and past storms is that provided by the Tropical Storm Risk Consortium (TSR). There are also seasonal forecasts & background information on the subject: the primary purpose of the site is to provide a risk assessment of storm activity in general and for specific disturbances:-
and another site with graphical visualisation of global tropical storms at:-