by the way VB.NET does NOT mean express edition
No mobile device development on that version whatsoever, you need the professional 2005 (dont say you dont as i have VB2003 standalone and it explicitly says that it cant)
i wont give you a particular topic, instead i would give an advice as you suggested. i feel you search within yourself, if you are good in more than one language then know the one you perform best in...thats one step
step 2: get a topic you know would be easy for you to complete and would make you learn something new, but bear in mind that the topic you choose should be worth being called a project.