Quick Boot is a good one. If you are connected via USB, you can also issue an adb reboot on the command line.
i use widgetsoid, which has that option built in, you can choose bootloader, recovery, normal reboot, etc.
HTH
If your looking for a Reboot program available to NON ROOTED device your options are very limited. Fast Reboot is one that I found for free on the Market and doesn't require root access (can be used on stock OS, no mods required).
QucikBootApp said:Reboot your phone quickly. Boot into Recovery and Bootloader with one tap.
** Root access to your phone is required to use this application. If you are not aware whether or not your phone has root access, you probably don't have root access. **