If you already have the Din opening...go ahead and put in another din unit. If you want the unit to just make noise into a couple of coaxials, the units own power should be more than sufficient.
If you want to upgrade and wander into the area of audiophile quality, might I suggest the 2 Pioneer head units with 2 USB inputs, Digital Signal Processing (if you are going for really great sound) and tons of high-end audio outputs in the Digital/Analog conversion stage.
It also has Blue Tooth which is really handy for Street Beats. Blue Tooth will not have the same qualify as Hi-Def or CD's. However, this unit does have the CD player built in and audiophile outputs in subs, mids and highs.
The DEH PRS-80 is the one I have as I didn't want to spend $1400 for the PRS-99 and has been around for a few years. 10 years ago you would have spent $2500 for this type of processing power and now you can get it for less than $250 bucks! Amazing...
While not quite as robust as the PRS-99...the 80 is more then adequate for tuning and great sound. A bit complicated to learn with the menus but after you get through the whole set-up...its not that bad. I believe they have the manual on-line but don't let that intimidate you.
I just checked on line and it's about $245 including shipping. That's about what I paid.
Here is a link to a page I have referenced previously: This guy knows his stuff and he tells you which brands to look for and which to avoid...he calls it the Good, Bad and the Ugly! Too funny...
Any of the brands in the top two categories should work really, really well. The Pioneer Unit I am referencing here...is the Stage 4 in the top category on his list. The faceplate is detachable to deter theft.
http://www.glasswolf.net/papers/goodbadugly.html