If Tom XAP Installer is not your cup of tea, here is another one for you ~ Multiple Xap Installer. It allows you to select multiple XAP files and deploy them to your phone or emulator. Besides, it includes XAP signing which required by downloaded XAP from Marketplace. Enable it at Settings when needed.
As same as Tom XAP Installer, Multiple Xap Installer requires unlocked Windows Phone 7 device, Windows PC with Microsoft .NET Framework 4 and Windows Phone SDK. Make sure that your phone was connected to PC with Zune launched. And phone is not in sleep mode.
Download Multiple Xap Installer v1.1 here.