[Bigsmith] Correct! Number 19 is, indeed, Rentaghost.

[rab] It's not the opening from Handel's Messiah is it?

Update:
1. Bob the dog - ISIHAC Theme 2. Chalky - Coronation Street 3. HB - Some Mothers Do 'Ave 'Em 4. Raak - Thunderbirds 5. Kim - The Archers' Theme 6. rab - Roobard and Custard 7. Bob the dog - Pomp and Curcumstance, Edward Elgar 8. Lib - Blind Date 9. ZK - Dangermouse 10. penelope - Blue Peter 11. Watty - Porridge 12. Kim - Tom & Jerry [Fred Quimby version] 13. Herr Bratsche - Monty Python 14. Raak - Star Trek 15. Bob the dog - Dr Who 16. rab - Have I Got News For You 17. Darren - Bergerac 18. Chalky - The Sweeney 19. Darren - Rentaghost 20. rab's plang-chonger - ???

[Darren] Nope. A hint?

No 21. Another TV theme. 80's/90's.
Do-dooo,do-do-do-do-do-doooooo
La-laaa, la-la-la-la-la-laaaaa-la [repeat lines 1 and 2]
Da-daaa-da, da-daaaa-da, da-da-da-da-da-daaaaa,
Da-daaa-da, da-daaaa-da, da-da-da-da-da-dahhhhhhhh, bom-bom-bom.