Wait a minute...
...before you start throwing money needlessly at this problem. A lot of the responses people have given are reasonable, but there were 2 points given (by lazyboy and shailat) that you should really work at before buying stuff that will likely muddy-up the situation rather than help.
Pretty much rule #1 in mixing - give each instrument (and voice is an instrument!) its own portion of the frequency spectrum. If something is not cutting thru in the mix, it's not likely it needs more effects (maybe some compression) - it probably has more to do with the fact that some other instrument is hogging the same portion of the audio spectrum. You don't want all the guitars to hog ALL the mids plus extend into the highs - use EQ to tame or restrict the frequency range. It's very possible that the guitars will sound like CRAP when solo'd, but sound amazing in the mix. You need to leave a hole in the sound spectrum for you vocal - then you'll have no trouble getting it to where it should be.
Pretty much rule #2 in mixing - if you've done your work following rule #1, then before you throw ANY effect into the mix, you should be able to get all the faders up and still have very reasonable, but dry-sounding mix. You add the verbs and stuff to give the dry sound some depth and dimension, and not so much to make their use obvious (unless it's an integral part of the sound - such as pronounced guitar delays). A well-proportioned mix (in terms of audio frequencies) will pretty much fly itself, then reach for effects to apply some space...
In addition, you reach for compression when a track's dynamic range is larger than normal when compared to another instrument it is being played against. For example with guitars and drums - in a live situation, the heavy guitar doesn't need compression in that situation because the drums will be heard very well and a drum's dynamic range is significantly wider than a guitar's is. In a recorded situation, the nature of recorded sound dictates that the guitar's range could APPARENTLY be equal to the recorded drum sounds - which is an unnatural sounding situation, requiring the use of a compressor to tame the guitar's range down to restore its relative balance to that of the drums. It's all a question of trying to maintain the dynamic relationship of recorded instruments to that of these same instruments being played live. Bear in mind, this "use of compression" theory borders pretty much on my own personal philosophy in recorded dynamics and some other engineers here may disagree, but you may still find it helpful.
Anyways - hope this helps..........
Bruce Valeriani
Blue Bear Sound