I can recommend this company: http://www.tme.eu/en/

I have had 2 pcb's made for the ATmega1284P-PU. On both PCB's I put the crystal and caps inside the socket. Never had any problems with uploading sketches. One of the PCB's I use in a small robot. I have uploaded hundreds of sketches to it while testing. I have 4 1284P-PU chips in use at the moment all with datecode 1216.
I now very little about designing PCB's. Is putting the crystal and caps inside the socket a bad design?

Did you change the xtal to a 20MHz one?

Yes, 20MHz crystal bought from Tayda Electronics. I tried 2 just to be sure. I also tried putting the chip on a breadboard with 20MHz crystal, caps, ... but got the same error. I can upload sketches through my USBasp but can not make a serial connection.

I get this:
Using Port                    : /dev/ttyUSB0
         Using Programmer              : arduino
         Overriding Baud Rate          : 250000
avrdude: serial_baud_lookup(): Using non-standard baud rate: 250000
avrdude: Send: 0 [30]   [20]
avrdude: Send: 0 [30]   [20]
avrdude: Send: 0 [30]   [20]
avrdude: ser_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding

Uploading sketches with the USBasp works.

From a previous post in this topic: http://arduino.cc/forum/index.php/topic,137902.msg1041577.html#msg1041577

I copied the code from that post to my boards.txt file, baud rate is set to 250000.

Today I tried getting an ATmega328P-PU to work at 20MHz. I downloaded the optiboot.zip file and copied the contents to my optiboot folder (I'm using Arduino-1.0.3 on linux). I made the necessary changes to boards.txt. I then started the Arduino ide and selected the "GVI High Speed (5V-20MHz-250k Baud)" board. Burned the bootloader with an USBasp, uploaded without errors. I then hooked up my ftdi usb/serial converter to the board and tried uploading the blink sketch. But no luck, it can't get serial communication. I tried another ftdi usb/serial converter but I got the same error:
avrdude: ser_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding

Just to be sure I plugged the chip in another board with a 16MHz crystal. Bootloaded the Uno bootloader and uploaded a couple of sketches, no problems there, so the chip is fine.

When I try uploading a sketch the led on pin 13 blinks a couple of times. So can I assume that the bootloader is working?

I bought a bunch of low resistance (5ohm & 10ohm) 10W cement resistors on Ebay.

Pic of my board: http://www.bajdi.com/wp-content/uploads/2012/12/bajduino-mega-3A.jpg

Interesting, I see you're using the 1284P chip here, which is the one people have been having all
the trouble with. So, you have an smt crystal and caps underneath the chip?

It's a 16MHz low profile through the hole crystal from Tayda electronics (I buy most of my stuff there). Inside the socket there is also a small inductor and capacitor (between vcc and avcc). 

A couple of months ago I had a PCB made for the ATmega1284 by Seeed. I've only been playing with electronics/Arduino for a year. So I was a bit nervous, would it work? To make it even more interesting it's powered by a LM2596 switch mode voltage regulator. I have now used the board extensively, uploaded hundreds of sketches and have not had any issues. Maybe I'm lucky? I even put the crystal and caps inside the socket. The board has an I2C logic level converter to talk to 3V3 I2C sensors and a header for a nRF24L01 wireless module. I have not tried uploading really big sketch. My biggest sketch is 30kb, anyone have an example of a really big sketch (+64kb) that I could upload?
Pic of my board: http://www.bajdi.com/wp-content/uploads/2012/12/bajduino-mega-3A.jpg

I see a regulator on that shield, that's probably a 3V3 regulator to power the Xbee... Look up the datasheet to see how much current it can give.

The designer of most Dagu products posts on the letsmakerobots.com forum. You could ask him there...

The Arduino Ethernet shield has its own 3.3V regulator.   

I started playing with micro controllers about one year ago. I originally planned to buy a couple of pic chips. Until I took a good look at the software/libraries available and compared it to Arduino. The learning curve for pics is a lot steeper. I'm sticking to Arduino/AVR, if you outgrow the Arduino IDE you can always use your favourite editor and use gcc-avr to compile your programs.  
This very forum also played a big role. I know there is always someone willing to help when I get stuck. I have learned a lot just by reading the programming section.

Search ebay or hobbyking for UBEC's. These devices will step down the voltage to 5 or 6V and are used in RC cars/planes to power the servos. Your local RC store will probably have some in stock... Most "RC" servo's are made for a max voltage of 6V.

Dit is mijn Rover 5: http://www.bajdi.com/?attachment_id=623
Ik heb er zelf een afstandsbediening voor gemaakt op basis van een Arduino http://www.bajdi.com/arduino-remote-control/remote-control/
Ik gebruik 2 wireless nRF24L01 modules voor de draadloze connectie.
Ondertussen heb ik ook een raspberryPi, mini webcam en wireless usb module gekocht. De bedoeling is om de beelden van de webcam door te sturen naar mijn pc via de raspberryPi. Een Arduino is daar niet krachtig genoeg voor. Dan heb ik ook de mogelijkheid om commando's van de raspberryPi door te sturen naar de Arduino.
Verwacht niet dat je dit even snel in elkaar steekt en programmeert, daar gaat behoorlijk veel tijd in