Southern Turku Archipelago
The southern part of the Sea of Archipelago is a little more popular than the Northern part. This is partly because its on the main Stockholm-Helsinki route, and partly because it has destinations like Gullkrona and Jurmo. In settled weather, in mid-July, the hotspots are full, but you don't need to go more than a couple of miles of the main track to find an empty spot.
Nauvo (Nagu)
Situated more or less in the centre of the archipelago, and a few hours south of Turku, Nauvo is a popular supply centre. The marina is pretty sheltered, except perhaps from the north, and is easy to enter, but watch out for (buoyed) shoals to starboard. Some of the moorings are odd too, as you nose the boat into a couple of rubber straps and then winch a rope from pontoon to stern (there's nothing astern to make fast to). These are best avoided by the bigger boats.
The marina is friendly and has good facilities, there are a number of restaurants and a reasonable supermarket.
Gullkrona
If you think Jurmo is good, Gullkrona is probably the spot in the whole of the archipelago. Its a private island, and when we were there was doing a roaring trade in 'Gullkrona' T-shirts and baseball hats, however there are interesting craft shops too. Best visited when things are not too busy.Note: I understand that Gullkrona is now open to visitors during the day, but you cannot stay overnight. Look out for local information.
Nötö
This is a little off the main tracks. We liked it because it was secluded and quiet when Jurmo was full. The quay is small, as is the shop, and you have to steer clear of the ferry, but there a couple of nice anchorages.
Some people may prefer the more popular fresh water lake at Björkö, a couple of miles to the south. This is a fully enclosed anchorage, with some places to tie to the shore.
Högsåra (Kejsarhamnen)
Just north of the village of Högsåra is a bay reputed to be used by the Russian Tsars. Apparently they used to arrive on their yachts and a couple of gun boats would guard the only two entrances to the bay. There's not much to show for that now, but its a very pretty anchorage with bags of room. There is a jetty at the south end of the bay with some stern buoys if you want to go ashore, but there is also plenty of space to anchor.
Kasnäs
A strategic spot on the route from south to north, and at one end of a national park, Kasnäs is another popular filling up centre. The marina is large, although some moorings on the outside are a little exposed.
The restaurant attached to the local Spa and conference centre is part of the Skärgårdssmak (Taste of the Archipelago) initiative and renowned for its food. There is a visitor centre giving information on the region.
Rosala
An ideal little harbour just off the main east-west track, there is both an organised guest harbour (with shops and restaurant) and plenty of room to anchor in the bay. There is a Viking centre in the village.
Rossala is a good overnight place en-route to Hanko. There is one decent anchorage nearby, but the entrance is tricky, and there is not much more before Hanko. (However Kasnäs is only a few miles away.)
Jurmo
In the right weather, this is the most popular spot in the archipelago. Jurmo is famous for its stone circles and rock fields. The island is mostly barren, due partly because the King of Sweden had it razed in the 1700s due to the naughty exploits of the islanders, who were using false lights to strand ships. Nowadays its an idyllic sandy destination. The marina is on the small side and gets crowded in high season.