My nephew loved anything that helped him walk around.  He started walking just around his first bday and liked his firetruck the most b/c he could use it to stand up, and then push it around to walk.

My nephew doesn't get overwhelmed - he gets bored :-D  If we only put out one or two toys, he plays with each for a few minutes then goes looking for more.  So we rotate him between half a dozen toys throughout his visits to keep him occupied.