I'm going to stay with my stock head unit and at some point add a small amp. What speakers are direct bolt in replacements for the stockers that you guys have used and could you tell much of a difference with just switching out the speakers. I did that on my Lincoln LS and it sounded better even without adding power.
Mine is an 05 supercab without audiophile, 6 disk, mp3 head unit.

 

6 X 8 is a direct replacement for all late model Ford vehicles....5 X 7 will also fit but why would anybody wanna do that? lol......even if you did have the adiophile system(which i believe has round speakers up front) you could still replace front speakers with 6 X 8 as the round speakers are just held in with a template that fits in the 6 X 8 spot.

 

With the stock unit, Alpine makes some nice 6x8's (or 5x7's)...and it will accomodate any upgrades in the future. You notice better highs and deeper bass. Whatever you do, dont buy anything that will be under powered...otherwise it wont sound good at all.

 

Ford utilizes a 6X8 speaker, but aftermarket 5X7's will almost always fit.

You have a lot of options for speakers. The reviews of speakers at Crutchfield.com are fairly good. The stock speakers are pitiful with paper cones, plastic chassis and rated at 25 watts. Almost any aftermarket speaker will improve the sound quality. The OEM stereo's deliver good power and clarity, they just need a quality set of speakers.

I've got a set of Infinity Reference component speakers in one F-150. A set of Infinity Reference 3-ways in another. My Sport Trac has a set of Polk Db's. The Infinity's really thump and have a ton of high end treble response. The Polk's deliver better mid range. I'd opt for something rated at 175 watts or higher.

For more bass, you can always slave in a powered sub-woofer with the OEM stereo.

 

I replaced my speakers with Alpine SPS-570A's and kept the OEM headunit. Sounds good for me they match the headunit output pretty well. Stick with the low power like sirshan said, prob no more than 40w. Seach ebay, think I got em for @ $60 a pair shipped. Don't bother with buying the speaker wire harnesses. I used the plugs off the OEM speakers and soldered them to the new speakers.

 

Boston Acoustics .....those are really the only two words you need to have in mind. You're gonna pay for 'em (about $179/pr), but worth every penny. I went to the most reputable car audio shop on Long Island, and the owner even took me to his car and removed the door panels to show me that he had them in HIS truck!

 

If you buy through Crutchfield, they give you free adapters for the OEM plugs to the aftermarket speakers. Look for the most effieceint set. Look for speakers that have a min to max RMS like 10w-60w (for example) which would match fine since that is about what the OEM head unit will do.

 

Crutchfield has a great buy on Alpine "Type R" SPR 574A, Regular $200 for $70, full Alpine warranty and as mentioned Crutchfield includes everything needed for hookup in your vehicle at no charge. They're perfect for using with a HU as they are rated to handle 5-35 watts RMS, and would be nice if you add a small amp later.

Also, http://www.mitekfactoryoutlet.com has a great buy on MTX 5x7s for $35.
They normally are $140 and have a 2 year warranty. Handle 40 watts RMS. Mitek Corporation is the parent company for MTX, xtant, Coustic, Streetwires, and others. Basically, you're buying factory direct. Probably a discontinued model or an overstock or some such thing. They do sell refurbs, but they are clearly designated as such. These are not refurbs.

The Alpine is a better speaker, but if using the HU as the sole amplification there would not be an astounding difference between the two.