I wouldn't ID 1 & 2 as ashtrays - these are called 'Zanfirico' items.
They were mostly decorative trinket dishes - many companies from Venini all the way down to modern Venetian ventures made these - I don't know the company that made either of yours.
1) Shallow bowl and the more desirable I think, it is beautifully crafted.
2) I have a few of these in many shapes, the pontil is usually roughly snapped off on old and new - the blue colour is very attractive.(http://img70.imageshack.us/img70/3017/latt2copy6xl.th.jpg)
From my own collection
3) is Murano even though it could be taken for Czech - the colours and the form are a give away - I have a similar one but with a silver Murano Importers label only - this shape goes in all sizes and all directions LOL
4) Looks like a nice controlled bubble ashtray - smooth base, well made, I love the way a bubble has been placed in each applied holder.
5) The rough base worries me, even the cheapest Italian glass is usually well finished - this could be of Eastern origin.
So I think two 'Zanfirico' dishes, two Murano ashtrays and something from Eastern shores.