Isla de la Luna
UPDATE June 2013. There are two companies that run boats from the harbour in Copacabana to Isla del Sol. One goes to the southern part (Yumani) (1.30 hours) and the other to the northern part (Challapampa) (2 hrs). Both leave Copacabana at 8.30 am and 1.30 pm. The morning boat to Yumani might continue to Isla de la Luna, if there are enough passengers, spend 1.5 hours there and then bring the passengers to Yumani (30 bs for the whole trip). Make sure you remind the boatman a few times that you will have 1.5 hours on Isla de la Luna, because he might drive slower (to save fuel) and then allow you only 40 minutes at the island, which is not enough.
From Yampupata local boatmen can take you across to Isla del Sol for 20 bs per person in a rowboat or for 150-200 bs per group of up to 7-8 people in a motorboat. A stop at Isla de la Luna can be negotiated.