First, you always need someone to monitor it - especially for your ceremony and special dances - to make sure that the right song is played at the right time and that the volume level and battery power is fine.
For your reception, it's hard to judge how people will react to music. Sometimes the crowd is just not getting on the floor and a DJ or band leader will know what to do to get them moving. As the bride and groom, it is not your job to MC your own wedding. However, if you have a friend or relative that you think can do the job, feel free to ask him or her to MC your wedding.
But remember this person is not a professional so you should try and ask someone who has MCed an event before to ensure that they know what they're doing. You'll also have to supply him or her with a list of special dances and do's and don'ts. (Ex: Don't start a conga line.)
If you're looking to cut your music budget, consider using your iPod for the ceremony and cocktail but hire a DJ or band for the reception. You can always limit the number of musicians to save money on a great band. But music can make or break a wedding reception, and it's important to have someone who knows what he/she is doing and can really get the crowd going.