A certain amount of broadcasts are normal. Firstly, any Windows machine (or a Linux machine pretending to be one using Samba etc) will send out UDP netbios broadcasts from time to time. Having other protocols (such as IPX) enabled increases this.

Secondly, any machine which has any IP traffic at all over ethernet to or from it will be sending out ARP messages from time to time. This is normal and is used to find other machines on the network.

Aside from those two, you shouldn't really see much unless you have other software which uses them. Neither should normally be blocked as it may cause existing stuff on your network to stop working. Neither sends any particularly sensitive information in broadcasts (Netbios sends machine and usernames, but nothing much more), so isn't a particular security hazard. Broadcasts are not normally routed anyway, so they won't go beyond your LAN.

DNS requests are, to the best of my knowledge, never broadcast so you should not see those.