Data Sheets for Selected Parts
If the data sheet you're looking for is not here, you'll have to do a bit of searching using keywords such as the manufacturer's name and any relevant ID number you can find on the part.

The information provided here is provided as convenience, but please note that the manufacturer's website should be consulted to ensure that information is up-to-date and accurate.

Microchip PICs
PIC16F87XA Datasheet (authoritative source) Microchip
PIC16F87XA Datasheet 16F87XA.pdf (4370K)
PIC Midrange Microcontroller Manual (old) PICMidrangeMicro.pdf (2711K)
PIC Midrange Microcontroller Manual (index page only) (authoritative source) Microchip
PIC16F877A Device Errata 16F877A_errata.pdf (159K)
PIC16F87X to PIC16F87XA Migration 16F87XtoA_migration.pdf (54K)

Atmel AVR
Atmega644 Datasheet Atmega644.pdf (4724K)
Atmega32 Datasheet (Authoritative Source) Atmel
Atmega32 Datasheet Atmega32.pdf (3200K)
Atmega32 Summary (Authoritative Source) Atmel
Atmega32 Summary Atmega32_summary.pdf (255K)

Microchip PICs - Deprecated (Used in Older Designs)
PIC16F87x micro-controller PIC16F87x.pdf (3827K)
PIC16F87x micro-controller (authoritative source) Microchip
PIC12C67x micro-controller PIC12C67x.pdf (1919K)
PIC12C67x micro-controller (authoritative source) Microchip

Other Commonly-Used Integrated Circuits
L293D Motor-Driver Chip (Texas Instruments) L293D_ti.pdf (92K)
L293D Motor-Driver Chip (SGS-Thomson) L293D_st.pdf (72K)
ICL7662 Inverter Chip ICL7662.pdf (88K)
ICL7660/2 Application Notes ICL7660-2.pdf (110K)
NCP7662 Inductorless Voltage Converter NCP7662.pdf (152K)
74HC595 8-bit Shift Register (Fairchild) 74HC595_fairchild.pdf (93K)
74HC595 8-bit Shift Register (Texas Instruments) 74HC595_ti.pdf (143K)
MAX232 RS-232 Serial Chip MAX232.pdf (442K)
78xx voltage regulators 78xx.pdf (155K)
TC4421 MOS-FET driver 2A/9Apk TC4421.pdf (72K)

ADCs and DACs
LTC1448 dual 12-bit DAC LTC1448.pdf (241K)
ADS8320 16-bit SPI ADC ADS8320.pdf (105K)
TLC2543 11-channel 12-bit SPI ADC TLC2543.pdf (412K)

Op-Amps and Rectifiers
MC33171/MC33172/MC33174 Op Amp MC33171-D.pdf (163K)
LM324 Quad OpAmp LM324.pdf (453K)
TL072/4 Dual/Quad OpAmp TL072-4.pdf (281K)
1N400x Axial Lead Standard Recovery Rectifier (ON Semiconductor) TL072-4.pdf (281K)

Transistors and Diodes
2N2219A Si NPN transistor 2N2219A.pdf (80K)
2N2905A Si PNP transistor 2N2905A.pdf (69K)
TIP12x Si power transistors (ST Microchips) TIP12x_st.pdf (53K)
TIP140 Si NPN power transistor TIP140.pdf (70K)
TIP145 Si PNP power transistor TIP145.pdf (69K)
2N4401 NPN general-purpose amplifier (Fairchild) 2N4401_fairchild.pdf (732K)
2N4401 NPN switching transistor (Philips) 2N4401_philips.pdf (52K)
2N4403 PNP general-purpose amplifier (Fairchild) 2N4403_fairchild.pdf (721K)
2N4403 PNP switching transistor (Philips) 2N4403_philips.pdf (52K)
1N4148/1N4448 high-speed diode (Philips) 1N4148_3.pdf (57K)

DC Motors
DCM-110 DCM-110.pdf (31K)
DCM-139 DCM-139.pdf (828K)
DCM-97 DCM-97.pdf (23K)

LCD Screens
DMC-50218 (Amtex) LCD_DMC-50218_amtex.pdf (156K)
DMC-50218 (Optrex) LCD_DMC-50218.pdf (166K)
Dot Matrix Character (DMC) LCD Manual (Optrex) LCD_DMCmanual.pdf (201K)

Infra Red Information
IS1U60 IR Receiver (Sharp) IS1U60.pdf (46K)
IR Emitter (Pink Colored QED523) QED522.pdf (383K)
IR Emitter (Purple Colored LD271) ld271.pdf (105K)
PNA460xM IR Receiver (Panasonic) PNA460xM.pdf (49K)
PNA461xM IR Receiver (Panasonic) PNA461xM.pdf (85K)
AIRRS (Analog Infra-Red Ranging System) User Manual Revison 1.1 AIRRS_1_1.pdf (131K)
AIRRS (Analog Infra-Red Ranging System) User Manual Revison 1.1 (authoritative source) HVWTech
DIRRS (Digital Infra-Red Ranging System) User Manual Revison 1.4 DIRRS_1_4.pdf (64K)
DIRRS (Digital Infra-Red Ranging System) User Manual Revison 1.4 (authoritative source) HVWTech
IrDA-Control PEK IrDA-Control_PEK.pdf (75K)
IrDA Control Host Controller IrDA_Control_Host.pdf (219K)

Miscellaneous Documents
Airpax Stepper Motor Catalog AirpaxCatalog.pdf (1504K)
Introduction to the Phase-Lock Loop PLLIntro.pdf (91K)
Dallas DAL1050 5-bit PWM 2-wire serial DAL1050.pdf (54K)
1-wire Rain Gauge RainGauge.pdf (385K)