I own TC-Helicon's VoiceLive2, which pretty much has all of their smaller boxes wrapped up into a single unit. I'll admit it's a little pricey, and you probably won't use all the features (unless you're into some pretty extreme stuff), but I'll go through some of my favourite features and recommend something in a lower price-point.
Just for context, you plug your mic into the pedal, and optionally an instrument as well (guitar or keyboard).
The "Tone" and "Pitch" buttons in the top left are probably my favourite features, mainly because they improve the vocals without a noticeable effect. Automatic compression, EQ, gating, de-essing, and very small (or large) pitch correction is added to the vocals when these are engaged.
Reverb, delay, double, and uMod is handy on this board as well if used tastefully in small amounts. It's capable of pretty extreme stuff, so you have to be careful not to overdo the effects.
The harmony feature is really cool. It generates voices in 3rds and 5ths above or below your own voice, following the chord changes that you play on guitar or keyboard. Although it's fun to play with, it doesn't follow perfectly all the time, and one wrong note makes for some really bad sounding voices so it can be risky to use this feature live. I would say it's more of a novelty to whip out an impress your friends rather than live use (however, it works beautifully with a keyboard running through MIDI).
This board does lots of other stuff (including looping), but I'll stop here and move on to recommendations.
Let's say my board broke tomorrow and I had to replace it with something else, I would get the TC-Helicon MicMechanic
It has all of my favourite features and effects that are actually useful for most genres, and they are exactly the same as the ones used in their Voicelive series.
As Anton mentioned, great mic choice with the SM58, however the biggest improvement you could probably make to your vocals right now would be a PA system of some kind. Your voice might be sounding thin due to the way the amp is reproducing lower frequencies of your vocals.