Fortnight means couple of weeks, right? (Sorry)

Gede Pangrango would be the obvious choice. It's not that hard to climb or so I heard. I don't know about reliable guides, but take a look at wisatacibodas[dot]com (bahasa only, translate with google) and contact the numbers/email.

Ujung Kulon is awfully far (for me) and relatively hard to reach from Jakarta. Anyway take a look at ujungkulontours[dot]com, it has english pages and seems to be good. If you planned to do some island hopping, ask them about the seastate (wave, current, etc) in your dates of visit.

The real hike of West Java, would be Mt. Ciremai. Base yourself in Cirebon (3 hr train from Jakarta).

ps: I don't really know the service quality of their guides, just pointing out some usable links. I am not really into mountaineering/outdoor trekking either, so can't help you with the details

And I think Bandung and its nearby area have a lot more to offer than a day trip. Bandung itself is just a city, but the surrounding areas are nice and there's a lot of interesting places.