Spring/Vintage:
Webley Junior Mk 1 or Mk 2; .177 pellet, small, simple and fun pistol
Diana/Original Model 6; .177 pellet, accurate, good build quality (recoiless)
Diana/Original Model 5; .177 pellet, accurate, good build quality (with recoil)
CO2:
Crosman 2240; .22, accurate, inexpensive, simple to use, easy to modify
Tau 7; .177, accurate, very nice balance, standard 12gm bulb
FWB Model 2; .177 pellet, accurate, simple to fill (bulk fill)
S&W 586-6; .177 pellet, accurate and fun 10 shot revolver
Tanfoglio/Swiss Arms/Remington 1911; 4.5mm BB, fun semi-automatic blowback.
SSP:
HW40; accurate, inexpensive .177
Baikal IZH 46M; accurate, easy cocking action, good fps, good balance.
PCP
PP700W; based on value/price, but need to fit sights! IIRC later models available with sights fitted.