Any artists/songs similar to Vivaldi?

Here's a broad answer (that assumes you aren't familiar with the different classical eras or with a wide array of classical composers):

http://en.wikipedia.org/wiki/Baroque#Music

I hope this is helpful!

One of the closest composers in style to Vivaldi is his compatriot and contemporary Antonio Caldara. However, Caldara wrote mostly opera and vocal music and so his music might not be what you are looking for. I would suggest other Italian Baroque composers for the sort of instrumental music you describe:

Geminiani

Locatelli

Manfredini

You can also try:

Fasch

Handel

Lully

Telemann

try Corelli or Torelli or Telemann.

or maybe even Handel.