The Guv is a good one. I have the MS100-BT and picked up some extra ODs (Sweet Honey Overdrive, Super Crunch Box & KLON Gold) and they are excellent, but I've gotten hooked on the Zoom reverb and delay sims especially the Ambience reverb which gives a bit a room to a flat sound and the Church reverb which sounds like the name.
The other reverbs that are more special effects that are great for backing someone that I've used are the Ice Delay and Shimmer both modeled on Strymon reverbs and the Particle verb. Really great sounds for when you have a lot of space in the music.