Take a look at my list I've put together, there are a few good second planes on there.

[link=http://www.rcuniverse.com/forum/m_4537845/tm.htm] Looking for a trainer- what's available. (Updated 1-19-07) [/link]

But recommendations about what you need. Sig 4-Stars are great, Sig Something Extra also make great second planes. Don't overlook the 4-stars, they are often under rated as aerobatic planes. They are forgiving as second planes, but can really perform well. And cutting off one bay off each wing really turns them loose. Ask Bubbagates, he flies IMAAC but he still has a 4-star that goes with him to the field all the time.

A Something Extra would be a great plane too. I've had 3 of them and they are great planes to start learning aerobatics one. They are quite capable of performing most of the more advanced aerobatic maneuvers, but can be tamed down as you learn.

The Sticks that others have mentioned here also make great transition planes for those wanting to move to aerobatics.

Others should be able to add more planes to the list of recommendations too.

Hope this helps

Ken