E.T. in the Senate
During the senate hearing, look over the Queen's shoulder at the bottom left of the screen. There will be a group of 4 or 5 E.T.'s (from the movie E.T. - The Extra Terrestrial) sitting together.
Millenium Falcon in Droid Ship Explosion?
When the droid control ship explodes, one large fragment is a model of the Millennium Falcon.
Vader's Suit in Watto's Shop
In the scene when Anakin, Qui-Gon and Watto are discussing entering the pod race, Qui-Gon and Watto are bargaining the conditions for entering. Look behind Qui-Gon as he speaks and you can see a shadow behind him on the wall of a black suit which is exactly like the one Darth Vader wears.
Hidden ILM in Palace
In the dramatically beautiful shot of the captured Queen Amidala gazing sadly out a window in Theed Palace wearing her red dress with orange lights around the bottom, off to the right hand side are the glowing orange letters "ILM" (Industrial Light and Magic, George Lucas' special effects company) near the base of one of the massive pillars.